Adding upstream version 3.0.36.upstream/3.0.36upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2757 insertions, 0 deletions

diff --git a/src/prompt_toolkit/layout/containers.py b/src/prompt_toolkit/layout/containers.py
new file mode 100644
index 0000000..03f9e7d
--- /dev/null
+++ b/src/prompt_toolkit/layout/containers.py
@@ -0,0 +1,2757 @@
+"""
+Container for the layout.
+(Containers can contain other containers or user interface controls.)
+"""
+from abc import ABCMeta, abstractmethod
+from enum import Enum
+from functools import partial
+from typing import (
+    TYPE_CHECKING,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Sequence,
+    Tuple,
+    Union,
+    cast,
+)
+
+from prompt_toolkit.application.current import get_app
+from prompt_toolkit.cache import SimpleCache
+from prompt_toolkit.data_structures import Point
+from prompt_toolkit.filters import (
+    FilterOrBool,
+    emacs_insert_mode,
+    to_filter,
+    vi_insert_mode,
+)
+from prompt_toolkit.formatted_text import (
+    AnyFormattedText,
+    StyleAndTextTuples,
+    to_formatted_text,
+)
+from prompt_toolkit.formatted_text.utils import (
+    fragment_list_to_text,
+    fragment_list_width,
+)
+from prompt_toolkit.key_binding import KeyBindingsBase
+from prompt_toolkit.mouse_events import MouseEvent, MouseEventType
+from prompt_toolkit.utils import get_cwidth, take_using_weights, to_int, to_str
+
+from .controls import (
+    DummyControl,
+    FormattedTextControl,
+    GetLinePrefixCallable,
+    UIContent,
+    UIControl,
+)
+from .dimension import (
+    AnyDimension,
+    Dimension,
+    max_layout_dimensions,
+    sum_layout_dimensions,
+    to_dimension,
+)
+from .margins import Margin
+from .mouse_handlers import MouseHandlers
+from .screen import _CHAR_CACHE, Screen, WritePosition
+from .utils import explode_text_fragments
+
+if TYPE_CHECKING:
+    from typing_extensions import Protocol, TypeGuard
+
+    from prompt_toolkit.key_binding.key_bindings import NotImplementedOrNone
+
+
+__all__ = [
+    "AnyContainer",
+    "Container",
+    "HorizontalAlign",
+    "VerticalAlign",
+    "HSplit",
+    "VSplit",
+    "FloatContainer",
+    "Float",
+    "WindowAlign",
+    "Window",
+    "WindowRenderInfo",
+    "ConditionalContainer",
+    "ScrollOffsets",
+    "ColorColumn",
+    "to_container",
+    "to_window",
+    "is_container",
+    "DynamicContainer",
+]
+
+
+class Container(metaclass=ABCMeta):
+    """
+    Base class for user interface layout.
+    """
+
+    @abstractmethod
+    def reset(self) -> None:
+        """
+        Reset the state of this container and all the children.
+        (E.g. reset scroll offsets, etc...)
+        """
+
+    @abstractmethod
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        """
+        Return a :class:`~prompt_toolkit.layout.Dimension` that represents the
+        desired width for this container.
+        """
+
+    @abstractmethod
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        """
+        Return a :class:`~prompt_toolkit.layout.Dimension` that represents the
+        desired height for this container.
+        """
+
+    @abstractmethod
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        """
+        Write the actual content to the screen.
+
+        :param screen: :class:`~prompt_toolkit.layout.screen.Screen`
+        :param mouse_handlers: :class:`~prompt_toolkit.layout.mouse_handlers.MouseHandlers`.
+        :param parent_style: Style string to pass to the :class:`.Window`
+            object. This will be applied to all content of the windows.
+            :class:`.VSplit` and :class:`.HSplit` can use it to pass their
+            style down to the windows that they contain.
+        :param z_index: Used for propagating z_index from parent to child.
+        """
+
+    def is_modal(self) -> bool:
+        """
+        When this container is modal, key bindings from parent containers are
+        not taken into account if a user control in this container is focused.
+        """
+        return False
+
+    def get_key_bindings(self) -> Optional[KeyBindingsBase]:
+        """
+        Returns a :class:`.KeyBindings` object. These bindings become active when any
+        user control in this container has the focus, except if any containers
+        between this container and the focused user control is modal.
+        """
+        return None
+
+    @abstractmethod
+    def get_children(self) -> List["Container"]:
+        """
+        Return the list of child :class:`.Container` objects.
+        """
+        return []
+
+
+if TYPE_CHECKING:
+
+    class MagicContainer(Protocol):
+        """
+        Any object that implements ``__pt_container__`` represents a container.
+        """
+
+        def __pt_container__(self) -> "AnyContainer":
+            ...
+
+
+AnyContainer = Union[Container, "MagicContainer"]
+
+
+def _window_too_small() -> "Window":
+    "Create a `Window` that displays the 'Window too small' text."
+    return Window(
+        FormattedTextControl(text=[("class:window-too-small", " Window too small... ")])
+    )
+
+
+class VerticalAlign(Enum):
+    "Alignment for `HSplit`."
+    TOP = "TOP"
+    CENTER = "CENTER"
+    BOTTOM = "BOTTOM"
+    JUSTIFY = "JUSTIFY"
+
+
+class HorizontalAlign(Enum):
+    "Alignment for `VSplit`."
+    LEFT = "LEFT"
+    CENTER = "CENTER"
+    RIGHT = "RIGHT"
+    JUSTIFY = "JUSTIFY"
+
+
+class _Split(Container):
+    """
+    The common parts of `VSplit` and `HSplit`.
+    """
+
+    def __init__(
+        self,
+        children: Sequence[AnyContainer],
+        window_too_small: Optional[Container] = None,
+        padding: AnyDimension = Dimension.exact(0),
+        padding_char: Optional[str] = None,
+        padding_style: str = "",
+        width: AnyDimension = None,
+        height: AnyDimension = None,
+        z_index: Optional[int] = None,
+        modal: bool = False,
+        key_bindings: Optional[KeyBindingsBase] = None,
+        style: Union[str, Callable[[], str]] = "",
+    ) -> None:
+
+        self.children = [to_container(c) for c in children]
+        self.window_too_small = window_too_small or _window_too_small()
+        self.padding = padding
+        self.padding_char = padding_char
+        self.padding_style = padding_style
+
+        self.width = width
+        self.height = height
+        self.z_index = z_index
+
+        self.modal = modal
+        self.key_bindings = key_bindings
+        self.style = style
+
+    def is_modal(self) -> bool:
+        return self.modal
+
+    def get_key_bindings(self) -> Optional[KeyBindingsBase]:
+        return self.key_bindings
+
+    def get_children(self) -> List[Container]:
+        return self.children
+
+
+class HSplit(_Split):
+    """
+    Several layouts, one stacked above/under the other. ::
+
+        +--------------------+
+        |                    |
+        +--------------------+
+        |                    |
+        +--------------------+
+
+    By default, this doesn't display a horizontal line between the children,
+    but if this is something you need, then create a HSplit as follows::
+
+        HSplit(children=[ ... ], padding_char='-',
+               padding=1, padding_style='#ffff00')
+
+    :param children: List of child :class:`.Container` objects.
+    :param window_too_small: A :class:`.Container` object that is displayed if
+        there is not enough space for all the children. By default, this is a
+        "Window too small" message.
+    :param align: `VerticalAlign` value.
+    :param width: When given, use this width instead of looking at the children.
+    :param height: When given, use this height instead of looking at the children.
+    :param z_index: (int or None) When specified, this can be used to bring
+        element in front of floating elements.  `None` means: inherit from parent.
+    :param style: A style string.
+    :param modal: ``True`` or ``False``.
+    :param key_bindings: ``None`` or a :class:`.KeyBindings` object.
+
+    :param padding: (`Dimension` or int), size to be used for the padding.
+    :param padding_char: Character to be used for filling in the padding.
+    :param padding_style: Style to applied to the padding.
+    """
+
+    def __init__(
+        self,
+        children: Sequence[AnyContainer],
+        window_too_small: Optional[Container] = None,
+        align: VerticalAlign = VerticalAlign.JUSTIFY,
+        padding: AnyDimension = 0,
+        padding_char: Optional[str] = None,
+        padding_style: str = "",
+        width: AnyDimension = None,
+        height: AnyDimension = None,
+        z_index: Optional[int] = None,
+        modal: bool = False,
+        key_bindings: Optional[KeyBindingsBase] = None,
+        style: Union[str, Callable[[], str]] = "",
+    ) -> None:
+
+        super().__init__(
+            children=children,
+            window_too_small=window_too_small,
+            padding=padding,
+            padding_char=padding_char,
+            padding_style=padding_style,
+            width=width,
+            height=height,
+            z_index=z_index,
+            modal=modal,
+            key_bindings=key_bindings,
+            style=style,
+        )
+
+        self.align = align
+
+        self._children_cache: SimpleCache[
+            Tuple[Container, ...], List[Container]
+        ] = SimpleCache(maxsize=1)
+        self._remaining_space_window = Window()  # Dummy window.
+
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        if self.width is not None:
+            return to_dimension(self.width)
+
+        if self.children:
+            dimensions = [c.preferred_width(max_available_width) for c in self.children]
+            return max_layout_dimensions(dimensions)
+        else:
+            return Dimension()
+
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        if self.height is not None:
+            return to_dimension(self.height)
+
+        dimensions = [
+            c.preferred_height(width, max_available_height) for c in self._all_children
+        ]
+        return sum_layout_dimensions(dimensions)
+
+    def reset(self) -> None:
+        for c in self.children:
+            c.reset()
+
+    @property
+    def _all_children(self) -> List[Container]:
+        """
+        List of child objects, including padding.
+        """
+
+        def get() -> List[Container]:
+            result: List[Container] = []
+
+            # Padding Top.
+            if self.align in (VerticalAlign.CENTER, VerticalAlign.BOTTOM):
+                result.append(Window(width=Dimension(preferred=0)))
+
+            # The children with padding.
+            for child in self.children:
+                result.append(child)
+                result.append(
+                    Window(
+                        height=self.padding,
+                        char=self.padding_char,
+                        style=self.padding_style,
+                    )
+                )
+            if result:
+                result.pop()
+
+            # Padding right.
+            if self.align in (VerticalAlign.CENTER, VerticalAlign.TOP):
+                result.append(Window(width=Dimension(preferred=0)))
+
+            return result
+
+        return self._children_cache.get(tuple(self.children), get)
+
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        """
+        Render the prompt to a `Screen` instance.
+
+        :param screen: The :class:`~prompt_toolkit.layout.screen.Screen` class
+            to which the output has to be written.
+        """
+        sizes = self._divide_heights(write_position)
+        style = parent_style + " " + to_str(self.style)
+        z_index = z_index if self.z_index is None else self.z_index
+
+        if sizes is None:
+            self.window_too_small.write_to_screen(
+                screen, mouse_handlers, write_position, style, erase_bg, z_index
+            )
+        else:
+            #
+            ypos = write_position.ypos
+            xpos = write_position.xpos
+            width = write_position.width
+
+            # Draw child panes.
+            for s, c in zip(sizes, self._all_children):
+                c.write_to_screen(
+                    screen,
+                    mouse_handlers,
+                    WritePosition(xpos, ypos, width, s),
+                    style,
+                    erase_bg,
+                    z_index,
+                )
+                ypos += s
+
+            # Fill in the remaining space. This happens when a child control
+            # refuses to take more space and we don't have any padding. Adding a
+            # dummy child control for this (in `self._all_children`) is not
+            # desired, because in some situations, it would take more space, even
+            # when it's not required. This is required to apply the styling.
+            remaining_height = write_position.ypos + write_position.height - ypos
+            if remaining_height > 0:
+                self._remaining_space_window.write_to_screen(
+                    screen,
+                    mouse_handlers,
+                    WritePosition(xpos, ypos, width, remaining_height),
+                    style,
+                    erase_bg,
+                    z_index,
+                )
+
+    def _divide_heights(self, write_position: WritePosition) -> Optional[List[int]]:
+        """
+        Return the heights for all rows.
+        Or None when there is not enough space.
+        """
+        if not self.children:
+            return []
+
+        width = write_position.width
+        height = write_position.height
+
+        # Calculate heights.
+        dimensions = [c.preferred_height(width, height) for c in self._all_children]
+
+        # Sum dimensions
+        sum_dimensions = sum_layout_dimensions(dimensions)
+
+        # If there is not enough space for both.
+        # Don't do anything.
+        if sum_dimensions.min > height:
+            return None
+
+        # Find optimal sizes. (Start with minimal size, increase until we cover
+        # the whole height.)
+        sizes = [d.min for d in dimensions]
+
+        child_generator = take_using_weights(
+            items=list(range(len(dimensions))), weights=[d.weight for d in dimensions]
+        )
+
+        i = next(child_generator)
+
+        # Increase until we meet at least the 'preferred' size.
+        preferred_stop = min(height, sum_dimensions.preferred)
+        preferred_dimensions = [d.preferred for d in dimensions]
+
+        while sum(sizes) < preferred_stop:
+            if sizes[i] < preferred_dimensions[i]:
+                sizes[i] += 1
+            i = next(child_generator)
+
+        # Increase until we use all the available space. (or until "max")
+        if not get_app().is_done:
+            max_stop = min(height, sum_dimensions.max)
+            max_dimensions = [d.max for d in dimensions]
+
+            while sum(sizes) < max_stop:
+                if sizes[i] < max_dimensions[i]:
+                    sizes[i] += 1
+                i = next(child_generator)
+
+        return sizes
+
+
+class VSplit(_Split):
+    """
+    Several layouts, one stacked left/right of the other. ::
+
+        +---------+----------+
+        |         |          |
+        |         |          |
+        +---------+----------+
+
+    By default, this doesn't display a vertical line between the children, but
+    if this is something you need, then create a HSplit as follows::
+
+        VSplit(children=[ ... ], padding_char='|',
+               padding=1, padding_style='#ffff00')
+
+    :param children: List of child :class:`.Container` objects.
+    :param window_too_small: A :class:`.Container` object that is displayed if
+        there is not enough space for all the children. By default, this is a
+        "Window too small" message.
+    :param align: `HorizontalAlign` value.
+    :param width: When given, use this width instead of looking at the children.
+    :param height: When given, use this height instead of looking at the children.
+    :param z_index: (int or None) When specified, this can be used to bring
+        element in front of floating elements.  `None` means: inherit from parent.
+    :param style: A style string.
+    :param modal: ``True`` or ``False``.
+    :param key_bindings: ``None`` or a :class:`.KeyBindings` object.
+
+    :param padding: (`Dimension` or int), size to be used for the padding.
+    :param padding_char: Character to be used for filling in the padding.
+    :param padding_style: Style to applied to the padding.
+    """
+
+    def __init__(
+        self,
+        children: Sequence[AnyContainer],
+        window_too_small: Optional[Container] = None,
+        align: HorizontalAlign = HorizontalAlign.JUSTIFY,
+        padding: AnyDimension = 0,
+        padding_char: Optional[str] = None,
+        padding_style: str = "",
+        width: AnyDimension = None,
+        height: AnyDimension = None,
+        z_index: Optional[int] = None,
+        modal: bool = False,
+        key_bindings: Optional[KeyBindingsBase] = None,
+        style: Union[str, Callable[[], str]] = "",
+    ) -> None:
+
+        super().__init__(
+            children=children,
+            window_too_small=window_too_small,
+            padding=padding,
+            padding_char=padding_char,
+            padding_style=padding_style,
+            width=width,
+            height=height,
+            z_index=z_index,
+            modal=modal,
+            key_bindings=key_bindings,
+            style=style,
+        )
+
+        self.align = align
+
+        self._children_cache: SimpleCache[
+            Tuple[Container, ...], List[Container]
+        ] = SimpleCache(maxsize=1)
+        self._remaining_space_window = Window()  # Dummy window.
+
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        if self.width is not None:
+            return to_dimension(self.width)
+
+        dimensions = [
+            c.preferred_width(max_available_width) for c in self._all_children
+        ]
+
+        return sum_layout_dimensions(dimensions)
+
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        if self.height is not None:
+            return to_dimension(self.height)
+
+        # At the point where we want to calculate the heights, the widths have
+        # already been decided. So we can trust `width` to be the actual
+        # `width` that's going to be used for the rendering. So,
+        # `divide_widths` is supposed to use all of the available width.
+        # Using only the `preferred` width caused a bug where the reported
+        # height was more than required. (we had a `BufferControl` which did
+        # wrap lines because of the smaller width returned by `_divide_widths`.
+
+        sizes = self._divide_widths(width)
+        children = self._all_children
+
+        if sizes is None:
+            return Dimension()
+        else:
+            dimensions = [
+                c.preferred_height(s, max_available_height)
+                for s, c in zip(sizes, children)
+            ]
+            return max_layout_dimensions(dimensions)
+
+    def reset(self) -> None:
+        for c in self.children:
+            c.reset()
+
+    @property
+    def _all_children(self) -> List[Container]:
+        """
+        List of child objects, including padding.
+        """
+
+        def get() -> List[Container]:
+            result: List[Container] = []
+
+            # Padding left.
+            if self.align in (HorizontalAlign.CENTER, HorizontalAlign.RIGHT):
+                result.append(Window(width=Dimension(preferred=0)))
+
+            # The children with padding.
+            for child in self.children:
+                result.append(child)
+                result.append(
+                    Window(
+                        width=self.padding,
+                        char=self.padding_char,
+                        style=self.padding_style,
+                    )
+                )
+            if result:
+                result.pop()
+
+            # Padding right.
+            if self.align in (HorizontalAlign.CENTER, HorizontalAlign.LEFT):
+                result.append(Window(width=Dimension(preferred=0)))
+
+            return result
+
+        return self._children_cache.get(tuple(self.children), get)
+
+    def _divide_widths(self, width: int) -> Optional[List[int]]:
+        """
+        Return the widths for all columns.
+        Or None when there is not enough space.
+        """
+        children = self._all_children
+
+        if not children:
+            return []
+
+        # Calculate widths.
+        dimensions = [c.preferred_width(width) for c in children]
+        preferred_dimensions = [d.preferred for d in dimensions]
+
+        # Sum dimensions
+        sum_dimensions = sum_layout_dimensions(dimensions)
+
+        # If there is not enough space for both.
+        # Don't do anything.
+        if sum_dimensions.min > width:
+            return None
+
+        # Find optimal sizes. (Start with minimal size, increase until we cover
+        # the whole width.)
+        sizes = [d.min for d in dimensions]
+
+        child_generator = take_using_weights(
+            items=list(range(len(dimensions))), weights=[d.weight for d in dimensions]
+        )
+
+        i = next(child_generator)
+
+        # Increase until we meet at least the 'preferred' size.
+        preferred_stop = min(width, sum_dimensions.preferred)
+
+        while sum(sizes) < preferred_stop:
+            if sizes[i] < preferred_dimensions[i]:
+                sizes[i] += 1
+            i = next(child_generator)
+
+        # Increase until we use all the available space.
+        max_dimensions = [d.max for d in dimensions]
+        max_stop = min(width, sum_dimensions.max)
+
+        while sum(sizes) < max_stop:
+            if sizes[i] < max_dimensions[i]:
+                sizes[i] += 1
+            i = next(child_generator)
+
+        return sizes
+
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        """
+        Render the prompt to a `Screen` instance.
+
+        :param screen: The :class:`~prompt_toolkit.layout.screen.Screen` class
+            to which the output has to be written.
+        """
+        if not self.children:
+            return
+
+        children = self._all_children
+        sizes = self._divide_widths(write_position.width)
+        style = parent_style + " " + to_str(self.style)
+        z_index = z_index if self.z_index is None else self.z_index
+
+        # If there is not enough space.
+        if sizes is None:
+            self.window_too_small.write_to_screen(
+                screen, mouse_handlers, write_position, style, erase_bg, z_index
+            )
+            return
+
+        # Calculate heights, take the largest possible, but not larger than
+        # write_position.height.
+        heights = [
+            child.preferred_height(width, write_position.height).preferred
+            for width, child in zip(sizes, children)
+        ]
+        height = max(write_position.height, min(write_position.height, max(heights)))
+
+        #
+        ypos = write_position.ypos
+        xpos = write_position.xpos
+
+        # Draw all child panes.
+        for s, c in zip(sizes, children):
+            c.write_to_screen(
+                screen,
+                mouse_handlers,
+                WritePosition(xpos, ypos, s, height),
+                style,
+                erase_bg,
+                z_index,
+            )
+            xpos += s
+
+        # Fill in the remaining space. This happens when a child control
+        # refuses to take more space and we don't have any padding. Adding a
+        # dummy child control for this (in `self._all_children`) is not
+        # desired, because in some situations, it would take more space, even
+        # when it's not required. This is required to apply the styling.
+        remaining_width = write_position.xpos + write_position.width - xpos
+        if remaining_width > 0:
+            self._remaining_space_window.write_to_screen(
+                screen,
+                mouse_handlers,
+                WritePosition(xpos, ypos, remaining_width, height),
+                style,
+                erase_bg,
+                z_index,
+            )
+
+
+class FloatContainer(Container):
+    """
+    Container which can contain another container for the background, as well
+    as a list of floating containers on top of it.
+
+    Example Usage::
+
+        FloatContainer(content=Window(...),
+                       floats=[
+                           Float(xcursor=True,
+                                ycursor=True,
+                                content=CompletionsMenu(...))
+                       ])
+
+    :param z_index: (int or None) When specified, this can be used to bring
+        element in front of floating elements.  `None` means: inherit from parent.
+        This is the z_index for the whole `Float` container as a whole.
+    """
+
+    def __init__(
+        self,
+        content: AnyContainer,
+        floats: List["Float"],
+        modal: bool = False,
+        key_bindings: Optional[KeyBindingsBase] = None,
+        style: Union[str, Callable[[], str]] = "",
+        z_index: Optional[int] = None,
+    ) -> None:
+
+        self.content = to_container(content)
+        self.floats = floats
+
+        self.modal = modal
+        self.key_bindings = key_bindings
+        self.style = style
+        self.z_index = z_index
+
+    def reset(self) -> None:
+        self.content.reset()
+
+        for f in self.floats:
+            f.content.reset()
+
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        return self.content.preferred_width(max_available_width)
+
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        """
+        Return the preferred height of the float container.
+        (We don't care about the height of the floats, they should always fit
+        into the dimensions provided by the container.)
+        """
+        return self.content.preferred_height(width, max_available_height)
+
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        style = parent_style + " " + to_str(self.style)
+        z_index = z_index if self.z_index is None else self.z_index
+
+        self.content.write_to_screen(
+            screen, mouse_handlers, write_position, style, erase_bg, z_index
+        )
+
+        for number, fl in enumerate(self.floats):
+            # z_index of a Float is computed by summing the z_index of the
+            # container and the `Float`.
+            new_z_index = (z_index or 0) + fl.z_index
+            style = parent_style + " " + to_str(self.style)
+
+            # If the float that we have here, is positioned relative to the
+            # cursor position, but the Window that specifies the cursor
+            # position is not drawn yet, because it's a Float itself, we have
+            # to postpone this calculation. (This is a work-around, but good
+            # enough for now.)
+            postpone = fl.xcursor is not None or fl.ycursor is not None
+
+            if postpone:
+                new_z_index = (
+                    number + 10**8
+                )  # Draw as late as possible, but keep the order.
+                screen.draw_with_z_index(
+                    z_index=new_z_index,
+                    draw_func=partial(
+                        self._draw_float,
+                        fl,
+                        screen,
+                        mouse_handlers,
+                        write_position,
+                        style,
+                        erase_bg,
+                        new_z_index,
+                    ),
+                )
+            else:
+                self._draw_float(
+                    fl,
+                    screen,
+                    mouse_handlers,
+                    write_position,
+                    style,
+                    erase_bg,
+                    new_z_index,
+                )
+
+    def _draw_float(
+        self,
+        fl: "Float",
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        "Draw a single Float."
+        # When a menu_position was given, use this instead of the cursor
+        # position. (These cursor positions are absolute, translate again
+        # relative to the write_position.)
+        # Note: This should be inside the for-loop, because one float could
+        #       set the cursor position to be used for the next one.
+        cpos = screen.get_menu_position(
+            fl.attach_to_window or get_app().layout.current_window
+        )
+        cursor_position = Point(
+            x=cpos.x - write_position.xpos, y=cpos.y - write_position.ypos
+        )
+
+        fl_width = fl.get_width()
+        fl_height = fl.get_height()
+        width: int
+        height: int
+        xpos: int
+        ypos: int
+
+        # Left & width given.
+        if fl.left is not None and fl_width is not None:
+            xpos = fl.left
+            width = fl_width
+        # Left & right given -> calculate width.
+        elif fl.left is not None and fl.right is not None:
+            xpos = fl.left
+            width = write_position.width - fl.left - fl.right
+        # Width & right given -> calculate left.
+        elif fl_width is not None and fl.right is not None:
+            xpos = write_position.width - fl.right - fl_width
+            width = fl_width
+        # Near x position of cursor.
+        elif fl.xcursor:
+            if fl_width is None:
+                width = fl.content.preferred_width(write_position.width).preferred
+                width = min(write_position.width, width)
+            else:
+                width = fl_width
+
+            xpos = cursor_position.x
+            if xpos + width > write_position.width:
+                xpos = max(0, write_position.width - width)
+        # Only width given -> center horizontally.
+        elif fl_width:
+            xpos = int((write_position.width - fl_width) / 2)
+            width = fl_width
+        # Otherwise, take preferred width from float content.
+        else:
+            width = fl.content.preferred_width(write_position.width).preferred
+
+            if fl.left is not None:
+                xpos = fl.left
+            elif fl.right is not None:
+                xpos = max(0, write_position.width - width - fl.right)
+            else:  # Center horizontally.
+                xpos = max(0, int((write_position.width - width) / 2))
+
+            # Trim.
+            width = min(width, write_position.width - xpos)
+
+        # Top & height given.
+        if fl.top is not None and fl_height is not None:
+            ypos = fl.top
+            height = fl_height
+        # Top & bottom given -> calculate height.
+        elif fl.top is not None and fl.bottom is not None:
+            ypos = fl.top
+            height = write_position.height - fl.top - fl.bottom
+        # Height & bottom given -> calculate top.
+        elif fl_height is not None and fl.bottom is not None:
+            ypos = write_position.height - fl_height - fl.bottom
+            height = fl_height
+        # Near cursor.
+        elif fl.ycursor:
+            ypos = cursor_position.y + (0 if fl.allow_cover_cursor else 1)
+
+            if fl_height is None:
+                height = fl.content.preferred_height(
+                    width, write_position.height
+                ).preferred
+            else:
+                height = fl_height
+
+            # Reduce height if not enough space. (We can use the height
+            # when the content requires it.)
+            if height > write_position.height - ypos:
+                if write_position.height - ypos + 1 >= ypos:
+                    # When the space below the cursor is more than
+                    # the space above, just reduce the height.
+                    height = write_position.height - ypos
+                else:
+                    # Otherwise, fit the float above the cursor.
+                    height = min(height, cursor_position.y)
+                    ypos = cursor_position.y - height
+
+        # Only height given -> center vertically.
+        elif fl_height:
+            ypos = int((write_position.height - fl_height) / 2)
+            height = fl_height
+        # Otherwise, take preferred height from content.
+        else:
+            height = fl.content.preferred_height(width, write_position.height).preferred
+
+            if fl.top is not None:
+                ypos = fl.top
+            elif fl.bottom is not None:
+                ypos = max(0, write_position.height - height - fl.bottom)
+            else:  # Center vertically.
+                ypos = max(0, int((write_position.height - height) / 2))
+
+            # Trim.
+            height = min(height, write_position.height - ypos)
+
+        # Write float.
+        # (xpos and ypos can be negative: a float can be partially visible.)
+        if height > 0 and width > 0:
+            wp = WritePosition(
+                xpos=xpos + write_position.xpos,
+                ypos=ypos + write_position.ypos,
+                width=width,
+                height=height,
+            )
+
+            if not fl.hide_when_covering_content or self._area_is_empty(screen, wp):
+                fl.content.write_to_screen(
+                    screen,
+                    mouse_handlers,
+                    wp,
+                    style,
+                    erase_bg=not fl.transparent(),
+                    z_index=z_index,
+                )
+
+    def _area_is_empty(self, screen: Screen, write_position: WritePosition) -> bool:
+        """
+        Return True when the area below the write position is still empty.
+        (For floats that should not hide content underneath.)
+        """
+        wp = write_position
+
+        for y in range(wp.ypos, wp.ypos + wp.height):
+            if y in screen.data_buffer:
+                row = screen.data_buffer[y]
+
+                for x in range(wp.xpos, wp.xpos + wp.width):
+                    c = row[x]
+                    if c.char != " ":
+                        return False
+
+        return True
+
+    def is_modal(self) -> bool:
+        return self.modal
+
+    def get_key_bindings(self) -> Optional[KeyBindingsBase]:
+        return self.key_bindings
+
+    def get_children(self) -> List[Container]:
+        children = [self.content]
+        children.extend(f.content for f in self.floats)
+        return children
+
+
+class Float:
+    """
+    Float for use in a :class:`.FloatContainer`.
+    Except for the `content` parameter, all other options are optional.
+
+    :param content: :class:`.Container` instance.
+
+    :param width: :class:`.Dimension` or callable which returns a :class:`.Dimension`.
+    :param height: :class:`.Dimension` or callable which returns a :class:`.Dimension`.
+
+    :param left: Distance to the left edge of the :class:`.FloatContainer`.
+    :param right: Distance to the right edge of the :class:`.FloatContainer`.
+    :param top: Distance to the top of the :class:`.FloatContainer`.
+    :param bottom: Distance to the bottom of the :class:`.FloatContainer`.
+
+    :param attach_to_window: Attach to the cursor from this window, instead of
+        the current window.
+    :param hide_when_covering_content: Hide the float when it covers content underneath.
+    :param allow_cover_cursor: When `False`, make sure to display the float
+        below the cursor. Not on top of the indicated position.
+    :param z_index: Z-index position. For a Float, this needs to be at least
+        one. It is relative to the z_index of the parent container.
+    :param transparent: :class:`.Filter` indicating whether this float needs to be
+        drawn transparently.
+    """
+
+    def __init__(
+        self,
+        content: AnyContainer,
+        top: Optional[int] = None,
+        right: Optional[int] = None,
+        bottom: Optional[int] = None,
+        left: Optional[int] = None,
+        width: Optional[Union[int, Callable[[], int]]] = None,
+        height: Optional[Union[int, Callable[[], int]]] = None,
+        xcursor: bool = False,
+        ycursor: bool = False,
+        attach_to_window: Optional[AnyContainer] = None,
+        hide_when_covering_content: bool = False,
+        allow_cover_cursor: bool = False,
+        z_index: int = 1,
+        transparent: bool = False,
+    ) -> None:
+
+        assert z_index >= 1
+
+        self.left = left
+        self.right = right
+        self.top = top
+        self.bottom = bottom
+
+        self.width = width
+        self.height = height
+
+        self.xcursor = xcursor
+        self.ycursor = ycursor
+
+        self.attach_to_window = (
+            to_window(attach_to_window) if attach_to_window else None
+        )
+
+        self.content = to_container(content)
+        self.hide_when_covering_content = hide_when_covering_content
+        self.allow_cover_cursor = allow_cover_cursor
+        self.z_index = z_index
+        self.transparent = to_filter(transparent)
+
+    def get_width(self) -> Optional[int]:
+        if callable(self.width):
+            return self.width()
+        return self.width
+
+    def get_height(self) -> Optional[int]:
+        if callable(self.height):
+            return self.height()
+        return self.height
+
+    def __repr__(self) -> str:
+        return "Float(content=%r)" % self.content
+
+
+class WindowRenderInfo:
+    """
+    Render information for the last render time of this control.
+    It stores mapping information between the input buffers (in case of a
+    :class:`~prompt_toolkit.layout.controls.BufferControl`) and the actual
+    render position on the output screen.
+
+    (Could be used for implementation of the Vi 'H' and 'L' key bindings as
+    well as implementing mouse support.)
+
+    :param ui_content: The original :class:`.UIContent` instance that contains
+        the whole input, without clipping. (ui_content)
+    :param horizontal_scroll: The horizontal scroll of the :class:`.Window` instance.
+    :param vertical_scroll: The vertical scroll of the :class:`.Window` instance.
+    :param window_width: The width of the window that displays the content,
+        without the margins.
+    :param window_height: The height of the window that displays the content.
+    :param configured_scroll_offsets: The scroll offsets as configured for the
+        :class:`Window` instance.
+    :param visible_line_to_row_col: Mapping that maps the row numbers on the
+        displayed screen (starting from zero for the first visible line) to
+        (row, col) tuples pointing to the row and column of the :class:`.UIContent`.
+    :param rowcol_to_yx: Mapping that maps (row, column) tuples representing
+        coordinates of the :class:`UIContent` to (y, x) absolute coordinates at
+        the rendered screen.
+    """
+
+    def __init__(
+        self,
+        window: "Window",
+        ui_content: UIContent,
+        horizontal_scroll: int,
+        vertical_scroll: int,
+        window_width: int,
+        window_height: int,
+        configured_scroll_offsets: "ScrollOffsets",
+        visible_line_to_row_col: Dict[int, Tuple[int, int]],
+        rowcol_to_yx: Dict[Tuple[int, int], Tuple[int, int]],
+        x_offset: int,
+        y_offset: int,
+        wrap_lines: bool,
+    ) -> None:
+
+        self.window = window
+        self.ui_content = ui_content
+        self.vertical_scroll = vertical_scroll
+        self.window_width = window_width  # Width without margins.
+        self.window_height = window_height
+
+        self.configured_scroll_offsets = configured_scroll_offsets
+        self.visible_line_to_row_col = visible_line_to_row_col
+        self.wrap_lines = wrap_lines
+
+        self._rowcol_to_yx = rowcol_to_yx  # row/col from input to absolute y/x
+        # screen coordinates.
+        self._x_offset = x_offset
+        self._y_offset = y_offset
+
+    @property
+    def visible_line_to_input_line(self) -> Dict[int, int]:
+        return {
+            visible_line: rowcol[0]
+            for visible_line, rowcol in self.visible_line_to_row_col.items()
+        }
+
+    @property
+    def cursor_position(self) -> Point:
+        """
+        Return the cursor position coordinates, relative to the left/top corner
+        of the rendered screen.
+        """
+        cpos = self.ui_content.cursor_position
+        try:
+            y, x = self._rowcol_to_yx[cpos.y, cpos.x]
+        except KeyError:
+            # For `DummyControl` for instance, the content can be empty, and so
+            # will `_rowcol_to_yx` be. Return 0/0 by default.
+            return Point(x=0, y=0)
+        else:
+            return Point(x=x - self._x_offset, y=y - self._y_offset)
+
+    @property
+    def applied_scroll_offsets(self) -> "ScrollOffsets":
+        """
+        Return a :class:`.ScrollOffsets` instance that indicates the actual
+        offset. This can be less than or equal to what's configured. E.g, when
+        the cursor is completely at the top, the top offset will be zero rather
+        than what's configured.
+        """
+        if self.displayed_lines[0] == 0:
+            top = 0
+        else:
+            # Get row where the cursor is displayed.
+            y = self.input_line_to_visible_line[self.ui_content.cursor_position.y]
+            top = min(y, self.configured_scroll_offsets.top)
+
+        return ScrollOffsets(
+            top=top,
+            bottom=min(
+                self.ui_content.line_count - self.displayed_lines[-1] - 1,
+                self.configured_scroll_offsets.bottom,
+            ),
+            # For left/right, it probably doesn't make sense to return something.
+            # (We would have to calculate the widths of all the lines and keep
+            # double width characters in mind.)
+            left=0,
+            right=0,
+        )
+
+    @property
+    def displayed_lines(self) -> List[int]:
+        """
+        List of all the visible rows. (Line numbers of the input buffer.)
+        The last line may not be entirely visible.
+        """
+        return sorted(row for row, col in self.visible_line_to_row_col.values())
+
+    @property
+    def input_line_to_visible_line(self) -> Dict[int, int]:
+        """
+        Return the dictionary mapping the line numbers of the input buffer to
+        the lines of the screen. When a line spans several rows at the screen,
+        the first row appears in the dictionary.
+        """
+        result: Dict[int, int] = {}
+        for k, v in self.visible_line_to_input_line.items():
+            if v in result:
+                result[v] = min(result[v], k)
+            else:
+                result[v] = k
+        return result
+
+    def first_visible_line(self, after_scroll_offset: bool = False) -> int:
+        """
+        Return the line number (0 based) of the input document that corresponds
+        with the first visible line.
+        """
+        if after_scroll_offset:
+            return self.displayed_lines[self.applied_scroll_offsets.top]
+        else:
+            return self.displayed_lines[0]
+
+    def last_visible_line(self, before_scroll_offset: bool = False) -> int:
+        """
+        Like `first_visible_line`, but for the last visible line.
+        """
+        if before_scroll_offset:
+            return self.displayed_lines[-1 - self.applied_scroll_offsets.bottom]
+        else:
+            return self.displayed_lines[-1]
+
+    def center_visible_line(
+        self, before_scroll_offset: bool = False, after_scroll_offset: bool = False
+    ) -> int:
+        """
+        Like `first_visible_line`, but for the center visible line.
+        """
+        return (
+            self.first_visible_line(after_scroll_offset)
+            + (
+                self.last_visible_line(before_scroll_offset)
+                - self.first_visible_line(after_scroll_offset)
+            )
+            // 2
+        )
+
+    @property
+    def content_height(self) -> int:
+        """
+        The full height of the user control.
+        """
+        return self.ui_content.line_count
+
+    @property
+    def full_height_visible(self) -> bool:
+        """
+        True when the full height is visible (There is no vertical scroll.)
+        """
+        return (
+            self.vertical_scroll == 0
+            and self.last_visible_line() == self.content_height
+        )
+
+    @property
+    def top_visible(self) -> bool:
+        """
+        True when the top of the buffer is visible.
+        """
+        return self.vertical_scroll == 0
+
+    @property
+    def bottom_visible(self) -> bool:
+        """
+        True when the bottom of the buffer is visible.
+        """
+        return self.last_visible_line() == self.content_height - 1
+
+    @property
+    def vertical_scroll_percentage(self) -> int:
+        """
+        Vertical scroll as a percentage. (0 means: the top is visible,
+        100 means: the bottom is visible.)
+        """
+        if self.bottom_visible:
+            return 100
+        else:
+            return 100 * self.vertical_scroll // self.content_height
+
+    def get_height_for_line(self, lineno: int) -> int:
+        """
+        Return the height of the given line.
+        (The height that it would take, if this line became visible.)
+        """
+        if self.wrap_lines:
+            return self.ui_content.get_height_for_line(
+                lineno, self.window_width, self.window.get_line_prefix
+            )
+        else:
+            return 1
+
+
+class ScrollOffsets:
+    """
+    Scroll offsets for the :class:`.Window` class.
+
+    Note that left/right offsets only make sense if line wrapping is disabled.
+    """
+
+    def __init__(
+        self,
+        top: Union[int, Callable[[], int]] = 0,
+        bottom: Union[int, Callable[[], int]] = 0,
+        left: Union[int, Callable[[], int]] = 0,
+        right: Union[int, Callable[[], int]] = 0,
+    ) -> None:
+
+        self._top = top
+        self._bottom = bottom
+        self._left = left
+        self._right = right
+
+    @property
+    def top(self) -> int:
+        return to_int(self._top)
+
+    @property
+    def bottom(self) -> int:
+        return to_int(self._bottom)
+
+    @property
+    def left(self) -> int:
+        return to_int(self._left)
+
+    @property
+    def right(self) -> int:
+        return to_int(self._right)
+
+    def __repr__(self) -> str:
+        return "ScrollOffsets(top={!r}, bottom={!r}, left={!r}, right={!r})".format(
+            self._top,
+            self._bottom,
+            self._left,
+            self._right,
+        )
+
+
+class ColorColumn:
+    """
+    Column for a :class:`.Window` to be colored.
+    """
+
+    def __init__(self, position: int, style: str = "class:color-column") -> None:
+        self.position = position
+        self.style = style
+
+
+_in_insert_mode = vi_insert_mode | emacs_insert_mode
+
+
+class WindowAlign(Enum):
+    """
+    Alignment of the Window content.
+
+    Note that this is different from `HorizontalAlign` and `VerticalAlign`,
+    which are used for the alignment of the child containers in respectively
+    `VSplit` and `HSplit`.
+    """
+
+    LEFT = "LEFT"
+    RIGHT = "RIGHT"
+    CENTER = "CENTER"
+
+
+class Window(Container):
+    """
+    Container that holds a control.
+
+    :param content: :class:`.UIControl` instance.
+    :param width: :class:`.Dimension` instance or callable.
+    :param height: :class:`.Dimension` instance or callable.
+    :param z_index: When specified, this can be used to bring element in front
+        of floating elements.
+    :param dont_extend_width: When `True`, don't take up more width then the
+                              preferred width reported by the control.
+    :param dont_extend_height: When `True`, don't take up more width then the
+                               preferred height reported by the control.
+    :param ignore_content_width: A `bool` or :class:`.Filter` instance. Ignore
+        the :class:`.UIContent` width when calculating the dimensions.
+    :param ignore_content_height: A `bool` or :class:`.Filter` instance. Ignore
+        the :class:`.UIContent` height when calculating the dimensions.
+    :param left_margins: A list of :class:`.Margin` instance to be displayed on
+        the left. For instance: :class:`~prompt_toolkit.layout.NumberedMargin`
+        can be one of them in order to show line numbers.
+    :param right_margins: Like `left_margins`, but on the other side.
+    :param scroll_offsets: :class:`.ScrollOffsets` instance, representing the
+        preferred amount of lines/columns to be always visible before/after the
+        cursor. When both top and bottom are a very high number, the cursor
+        will be centered vertically most of the time.
+    :param allow_scroll_beyond_bottom: A `bool` or
+        :class:`.Filter` instance. When True, allow scrolling so far, that the
+        top part of the content is not visible anymore, while there is still
+        empty space available at the bottom of the window. In the Vi editor for
+        instance, this is possible. You will see tildes while the top part of
+        the body is hidden.
+    :param wrap_lines: A `bool` or :class:`.Filter` instance. When True, don't
+        scroll horizontally, but wrap lines instead.
+    :param get_vertical_scroll: Callable that takes this window
+        instance as input and returns a preferred vertical scroll.
+        (When this is `None`, the scroll is only determined by the last and
+        current cursor position.)
+    :param get_horizontal_scroll: Callable that takes this window
+        instance as input and returns a preferred vertical scroll.
+    :param always_hide_cursor: A `bool` or
+        :class:`.Filter` instance. When True, never display the cursor, even
+        when the user control specifies a cursor position.
+    :param cursorline: A `bool` or :class:`.Filter` instance. When True,
+        display a cursorline.
+    :param cursorcolumn: A `bool` or :class:`.Filter` instance. When True,
+        display a cursorcolumn.
+    :param colorcolumns: A list of :class:`.ColorColumn` instances that
+        describe the columns to be highlighted, or a callable that returns such
+        a list.
+    :param align: :class:`.WindowAlign` value or callable that returns an
+        :class:`.WindowAlign` value. alignment of content.
+    :param style: A style string. Style to be applied to all the cells in this
+        window. (This can be a callable that returns a string.)
+    :param char: (string) Character to be used for filling the background. This
+        can also be a callable that returns a character.
+    :param get_line_prefix: None or a callable that returns formatted text to
+        be inserted before a line. It takes a line number (int) and a
+        wrap_count and returns formatted text. This can be used for
+        implementation of line continuations, things like Vim "breakindent" and
+        so on.
+    """
+
+    def __init__(
+        self,
+        content: Optional[UIControl] = None,
+        width: AnyDimension = None,
+        height: AnyDimension = None,
+        z_index: Optional[int] = None,
+        dont_extend_width: FilterOrBool = False,
+        dont_extend_height: FilterOrBool = False,
+        ignore_content_width: FilterOrBool = False,
+        ignore_content_height: FilterOrBool = False,
+        left_margins: Optional[Sequence[Margin]] = None,
+        right_margins: Optional[Sequence[Margin]] = None,
+        scroll_offsets: Optional[ScrollOffsets] = None,
+        allow_scroll_beyond_bottom: FilterOrBool = False,
+        wrap_lines: FilterOrBool = False,
+        get_vertical_scroll: Optional[Callable[["Window"], int]] = None,
+        get_horizontal_scroll: Optional[Callable[["Window"], int]] = None,
+        always_hide_cursor: FilterOrBool = False,
+        cursorline: FilterOrBool = False,
+        cursorcolumn: FilterOrBool = False,
+        colorcolumns: Union[
+            None, List[ColorColumn], Callable[[], List[ColorColumn]]
+        ] = None,
+        align: Union[WindowAlign, Callable[[], WindowAlign]] = WindowAlign.LEFT,
+        style: Union[str, Callable[[], str]] = "",
+        char: Union[None, str, Callable[[], str]] = None,
+        get_line_prefix: Optional[GetLinePrefixCallable] = None,
+    ) -> None:
+
+        self.allow_scroll_beyond_bottom = to_filter(allow_scroll_beyond_bottom)
+        self.always_hide_cursor = to_filter(always_hide_cursor)
+        self.wrap_lines = to_filter(wrap_lines)
+        self.cursorline = to_filter(cursorline)
+        self.cursorcolumn = to_filter(cursorcolumn)
+
+        self.content = content or DummyControl()
+        self.dont_extend_width = to_filter(dont_extend_width)
+        self.dont_extend_height = to_filter(dont_extend_height)
+        self.ignore_content_width = to_filter(ignore_content_width)
+        self.ignore_content_height = to_filter(ignore_content_height)
+        self.left_margins = left_margins or []
+        self.right_margins = right_margins or []
+        self.scroll_offsets = scroll_offsets or ScrollOffsets()
+        self.get_vertical_scroll = get_vertical_scroll
+        self.get_horizontal_scroll = get_horizontal_scroll
+        self.colorcolumns = colorcolumns or []
+        self.align = align
+        self.style = style
+        self.char = char
+        self.get_line_prefix = get_line_prefix
+
+        self.width = width
+        self.height = height
+        self.z_index = z_index
+
+        # Cache for the screens generated by the margin.
+        self._ui_content_cache: SimpleCache[
+            Tuple[int, int, int], UIContent
+        ] = SimpleCache(maxsize=8)
+        self._margin_width_cache: SimpleCache[Tuple[Margin, int], int] = SimpleCache(
+            maxsize=1
+        )
+
+        self.reset()
+
+    def __repr__(self) -> str:
+        return "Window(content=%r)" % self.content
+
+    def reset(self) -> None:
+        self.content.reset()
+
+        #: Scrolling position of the main content.
+        self.vertical_scroll = 0
+        self.horizontal_scroll = 0
+
+        # Vertical scroll 2: this is the vertical offset that a line is
+        # scrolled if a single line (the one that contains the cursor) consumes
+        # all of the vertical space.
+        self.vertical_scroll_2 = 0
+
+        #: Keep render information (mappings between buffer input and render
+        #: output.)
+        self.render_info: Optional[WindowRenderInfo] = None
+
+    def _get_margin_width(self, margin: Margin) -> int:
+        """
+        Return the width for this margin.
+        (Calculate only once per render time.)
+        """
+        # Margin.get_width, needs to have a UIContent instance.
+        def get_ui_content() -> UIContent:
+            return self._get_ui_content(width=0, height=0)
+
+        def get_width() -> int:
+            return margin.get_width(get_ui_content)
+
+        key = (margin, get_app().render_counter)
+        return self._margin_width_cache.get(key, get_width)
+
+    def _get_total_margin_width(self) -> int:
+        """
+        Calculate and return the width of the margin (left + right).
+        """
+        return sum(self._get_margin_width(m) for m in self.left_margins) + sum(
+            self._get_margin_width(m) for m in self.right_margins
+        )
+
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        """
+        Calculate the preferred width for this window.
+        """
+
+        def preferred_content_width() -> Optional[int]:
+            """Content width: is only calculated if no exact width for the
+            window was given."""
+            if self.ignore_content_width():
+                return None
+
+            # Calculate the width of the margin.
+            total_margin_width = self._get_total_margin_width()
+
+            # Window of the content. (Can be `None`.)
+            preferred_width = self.content.preferred_width(
+                max_available_width - total_margin_width
+            )
+
+            if preferred_width is not None:
+                # Include width of the margins.
+                preferred_width += total_margin_width
+            return preferred_width
+
+        # Merge.
+        return self._merge_dimensions(
+            dimension=to_dimension(self.width),
+            get_preferred=preferred_content_width,
+            dont_extend=self.dont_extend_width(),
+        )
+
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        """
+        Calculate the preferred height for this window.
+        """
+
+        def preferred_content_height() -> Optional[int]:
+            """Content height: is only calculated if no exact height for the
+            window was given."""
+            if self.ignore_content_height():
+                return None
+
+            total_margin_width = self._get_total_margin_width()
+            wrap_lines = self.wrap_lines()
+
+            return self.content.preferred_height(
+                width - total_margin_width,
+                max_available_height,
+                wrap_lines,
+                self.get_line_prefix,
+            )
+
+        return self._merge_dimensions(
+            dimension=to_dimension(self.height),
+            get_preferred=preferred_content_height,
+            dont_extend=self.dont_extend_height(),
+        )
+
+    @staticmethod
+    def _merge_dimensions(
+        dimension: Optional[Dimension],
+        get_preferred: Callable[[], Optional[int]],
+        dont_extend: bool = False,
+    ) -> Dimension:
+        """
+        Take the Dimension from this `Window` class and the received preferred
+        size from the `UIControl` and return a `Dimension` to report to the
+        parent container.
+        """
+        dimension = dimension or Dimension()
+
+        # When a preferred dimension was explicitly given to the Window,
+        # ignore the UIControl.
+        preferred: Optional[int]
+
+        if dimension.preferred_specified:
+            preferred = dimension.preferred
+        else:
+            # Otherwise, calculate the preferred dimension from the UI control
+            # content.
+            preferred = get_preferred()
+
+        # When a 'preferred' dimension is given by the UIControl, make sure
+        # that it stays within the bounds of the Window.
+        if preferred is not None:
+            if dimension.max_specified:
+                preferred = min(preferred, dimension.max)
+
+            if dimension.min_specified:
+                preferred = max(preferred, dimension.min)
+
+        # When a `dont_extend` flag has been given, use the preferred dimension
+        # also as the max dimension.
+        max_: Optional[int]
+        min_: Optional[int]
+
+        if dont_extend and preferred is not None:
+            max_ = min(dimension.max, preferred)
+        else:
+            max_ = dimension.max if dimension.max_specified else None
+
+        min_ = dimension.min if dimension.min_specified else None
+
+        return Dimension(
+            min=min_, max=max_, preferred=preferred, weight=dimension.weight
+        )
+
+    def _get_ui_content(self, width: int, height: int) -> UIContent:
+        """
+        Create a `UIContent` instance.
+        """
+
+        def get_content() -> UIContent:
+            return self.content.create_content(width=width, height=height)
+
+        key = (get_app().render_counter, width, height)
+        return self._ui_content_cache.get(key, get_content)
+
+    def _get_digraph_char(self) -> Optional[str]:
+        "Return `False`, or the Digraph symbol to be used."
+        app = get_app()
+        if app.quoted_insert:
+            return "^"
+        if app.vi_state.waiting_for_digraph:
+            if app.vi_state.digraph_symbol1:
+                return app.vi_state.digraph_symbol1
+            return "?"
+        return None
+
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        """
+        Write window to screen. This renders the user control, the margins and
+        copies everything over to the absolute position at the given screen.
+        """
+        # If dont_extend_width/height was given. Then reduce width/height in
+        # WritePosition if the parent wanted us to paint in a bigger area.
+        # (This happens if this window is bundled with another window in a
+        # HSplit/VSplit, but with different size requirements.)
+        write_position = WritePosition(
+            xpos=write_position.xpos,
+            ypos=write_position.ypos,
+            width=write_position.width,
+            height=write_position.height,
+        )
+
+        if self.dont_extend_width():
+            write_position.width = min(
+                write_position.width,
+                self.preferred_width(write_position.width).preferred,
+            )
+
+        if self.dont_extend_height():
+            write_position.height = min(
+                write_position.height,
+                self.preferred_height(
+                    write_position.width, write_position.height
+                ).preferred,
+            )
+
+        # Draw
+        z_index = z_index if self.z_index is None else self.z_index
+
+        draw_func = partial(
+            self._write_to_screen_at_index,
+            screen,
+            mouse_handlers,
+            write_position,
+            parent_style,
+            erase_bg,
+        )
+
+        if z_index is None or z_index <= 0:
+            # When no z_index is given, draw right away.
+            draw_func()
+        else:
+            # Otherwise, postpone.
+            screen.draw_with_z_index(z_index=z_index, draw_func=draw_func)
+
+    def _write_to_screen_at_index(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+    ) -> None:
+        # Don't bother writing invisible windows.
+        # (We save some time, but also avoid applying last-line styling.)
+        if write_position.height <= 0 or write_position.width <= 0:
+            return
+
+        # Calculate margin sizes.
+        left_margin_widths = [self._get_margin_width(m) for m in self.left_margins]
+        right_margin_widths = [self._get_margin_width(m) for m in self.right_margins]
+        total_margin_width = sum(left_margin_widths + right_margin_widths)
+
+        # Render UserControl.
+        ui_content = self.content.create_content(
+            write_position.width - total_margin_width, write_position.height
+        )
+        assert isinstance(ui_content, UIContent)
+
+        # Scroll content.
+        wrap_lines = self.wrap_lines()
+        self._scroll(
+            ui_content, write_position.width - total_margin_width, write_position.height
+        )
+
+        # Erase background and fill with `char`.
+        self._fill_bg(screen, write_position, erase_bg)
+
+        # Resolve `align` attribute.
+        align = self.align() if callable(self.align) else self.align
+
+        # Write body
+        visible_line_to_row_col, rowcol_to_yx = self._copy_body(
+            ui_content,
+            screen,
+            write_position,
+            sum(left_margin_widths),
+            write_position.width - total_margin_width,
+            self.vertical_scroll,
+            self.horizontal_scroll,
+            wrap_lines=wrap_lines,
+            highlight_lines=True,
+            vertical_scroll_2=self.vertical_scroll_2,
+            always_hide_cursor=self.always_hide_cursor(),
+            has_focus=get_app().layout.current_control == self.content,
+            align=align,
+            get_line_prefix=self.get_line_prefix,
+        )
+
+        # Remember render info. (Set before generating the margins. They need this.)
+        x_offset = write_position.xpos + sum(left_margin_widths)
+        y_offset = write_position.ypos
+
+        render_info = WindowRenderInfo(
+            window=self,
+            ui_content=ui_content,
+            horizontal_scroll=self.horizontal_scroll,
+            vertical_scroll=self.vertical_scroll,
+            window_width=write_position.width - total_margin_width,
+            window_height=write_position.height,
+            configured_scroll_offsets=self.scroll_offsets,
+            visible_line_to_row_col=visible_line_to_row_col,
+            rowcol_to_yx=rowcol_to_yx,
+            x_offset=x_offset,
+            y_offset=y_offset,
+            wrap_lines=wrap_lines,
+        )
+        self.render_info = render_info
+
+        # Set mouse handlers.
+        def mouse_handler(mouse_event: MouseEvent) -> "NotImplementedOrNone":
+            """
+            Wrapper around the mouse_handler of the `UIControl` that turns
+            screen coordinates into line coordinates.
+            Returns `NotImplemented` if no UI invalidation should be done.
+            """
+            # Don't handle mouse events outside of the current modal part of
+            # the UI.
+            if self not in get_app().layout.walk_through_modal_area():
+                return NotImplemented
+
+            # Find row/col position first.
+            yx_to_rowcol = {v: k for k, v in rowcol_to_yx.items()}
+            y = mouse_event.position.y
+            x = mouse_event.position.x
+
+            # If clicked below the content area, look for a position in the
+            # last line instead.
+            max_y = write_position.ypos + len(visible_line_to_row_col) - 1
+            y = min(max_y, y)
+            result: NotImplementedOrNone
+
+            while x >= 0:
+                try:
+                    row, col = yx_to_rowcol[y, x]
+                except KeyError:
+                    # Try again. (When clicking on the right side of double
+                    # width characters, or on the right side of the input.)
+                    x -= 1
+                else:
+                    # Found position, call handler of UIControl.
+                    result = self.content.mouse_handler(
+                        MouseEvent(
+                            position=Point(x=col, y=row),
+                            event_type=mouse_event.event_type,
+                            button=mouse_event.button,
+                            modifiers=mouse_event.modifiers,
+                        )
+                    )
+                    break
+            else:
+                # nobreak.
+                # (No x/y coordinate found for the content. This happens in
+                # case of a DummyControl, that does not have any content.
+                # Report (0,0) instead.)
+                result = self.content.mouse_handler(
+                    MouseEvent(
+                        position=Point(x=0, y=0),
+                        event_type=mouse_event.event_type,
+                        button=mouse_event.button,
+                        modifiers=mouse_event.modifiers,
+                    )
+                )
+
+            # If it returns NotImplemented, handle it here.
+            if result == NotImplemented:
+                result = self._mouse_handler(mouse_event)
+
+            return result
+
+        mouse_handlers.set_mouse_handler_for_range(
+            x_min=write_position.xpos + sum(left_margin_widths),
+            x_max=write_position.xpos + write_position.width - total_margin_width,
+            y_min=write_position.ypos,
+            y_max=write_position.ypos + write_position.height,
+            handler=mouse_handler,
+        )
+
+        # Render and copy margins.
+        move_x = 0
+
+        def render_margin(m: Margin, width: int) -> UIContent:
+            "Render margin. Return `Screen`."
+            # Retrieve margin fragments.
+            fragments = m.create_margin(render_info, width, write_position.height)
+
+            # Turn it into a UIContent object.
+            # already rendered those fragments using this size.)
+            return FormattedTextControl(fragments).create_content(
+                width + 1, write_position.height
+            )
+
+        for m, width in zip(self.left_margins, left_margin_widths):
+            if width > 0:  # (ConditionalMargin returns a zero width. -- Don't render.)
+                # Create screen for margin.
+                margin_content = render_margin(m, width)
+
+                # Copy and shift X.
+                self._copy_margin(margin_content, screen, write_position, move_x, width)
+                move_x += width
+
+        move_x = write_position.width - sum(right_margin_widths)
+
+        for m, width in zip(self.right_margins, right_margin_widths):
+            # Create screen for margin.
+            margin_content = render_margin(m, width)
+
+            # Copy and shift X.
+            self._copy_margin(margin_content, screen, write_position, move_x, width)
+            move_x += width
+
+        # Apply 'self.style'
+        self._apply_style(screen, write_position, parent_style)
+
+        # Tell the screen that this user control has been painted at this
+        # position.
+        screen.visible_windows_to_write_positions[self] = write_position
+
+    def _copy_body(
+        self,
+        ui_content: UIContent,
+        new_screen: Screen,
+        write_position: WritePosition,
+        move_x: int,
+        width: int,
+        vertical_scroll: int = 0,
+        horizontal_scroll: int = 0,
+        wrap_lines: bool = False,
+        highlight_lines: bool = False,
+        vertical_scroll_2: int = 0,
+        always_hide_cursor: bool = False,
+        has_focus: bool = False,
+        align: WindowAlign = WindowAlign.LEFT,
+        get_line_prefix: Optional[Callable[[int, int], AnyFormattedText]] = None,
+    ) -> Tuple[Dict[int, Tuple[int, int]], Dict[Tuple[int, int], Tuple[int, int]]]:
+        """
+        Copy the UIContent into the output screen.
+        Return (visible_line_to_row_col, rowcol_to_yx) tuple.
+
+        :param get_line_prefix: None or a callable that takes a line number
+            (int) and a wrap_count (int) and returns formatted text.
+        """
+        xpos = write_position.xpos + move_x
+        ypos = write_position.ypos
+        line_count = ui_content.line_count
+        new_buffer = new_screen.data_buffer
+        empty_char = _CHAR_CACHE["", ""]
+
+        # Map visible line number to (row, col) of input.
+        # 'col' will always be zero if line wrapping is off.
+        visible_line_to_row_col: Dict[int, Tuple[int, int]] = {}
+
+        # Maps (row, col) from the input to (y, x) screen coordinates.
+        rowcol_to_yx: Dict[Tuple[int, int], Tuple[int, int]] = {}
+
+        def copy_line(
+            line: StyleAndTextTuples,
+            lineno: int,
+            x: int,
+            y: int,
+            is_input: bool = False,
+        ) -> Tuple[int, int]:
+            """
+            Copy over a single line to the output screen. This can wrap over
+            multiple lines in the output. It will call the prefix (prompt)
+            function before every line.
+            """
+            if is_input:
+                current_rowcol_to_yx = rowcol_to_yx
+            else:
+                current_rowcol_to_yx = {}  # Throwaway dictionary.
+
+            # Draw line prefix.
+            if is_input and get_line_prefix:
+                prompt = to_formatted_text(get_line_prefix(lineno, 0))
+                x, y = copy_line(prompt, lineno, x, y, is_input=False)
+
+            # Scroll horizontally.
+            skipped = 0  # Characters skipped because of horizontal scrolling.
+            if horizontal_scroll and is_input:
+                h_scroll = horizontal_scroll
+                line = explode_text_fragments(line)
+                while h_scroll > 0 and line:
+                    h_scroll -= get_cwidth(line[0][1])
+                    skipped += 1
+                    del line[:1]  # Remove first character.
+
+                x -= h_scroll  # When scrolling over double width character,
+                # this can end up being negative.
+
+            # Align this line. (Note that this doesn't work well when we use
+            # get_line_prefix and that function returns variable width prefixes.)
+            if align == WindowAlign.CENTER:
+                line_width = fragment_list_width(line)
+                if line_width < width:
+                    x += (width - line_width) // 2
+            elif align == WindowAlign.RIGHT:
+                line_width = fragment_list_width(line)
+                if line_width < width:
+                    x += width - line_width
+
+            col = 0
+            wrap_count = 0
+            for style, text, *_ in line:
+                new_buffer_row = new_buffer[y + ypos]
+
+                # Remember raw VT escape sequences. (E.g. FinalTerm's
+                # escape sequences.)
+                if "[ZeroWidthEscape]" in style:
+                    new_screen.zero_width_escapes[y + ypos][x + xpos] += text
+                    continue
+
+                for c in text:
+                    char = _CHAR_CACHE[c, style]
+                    char_width = char.width
+
+                    # Wrap when the line width is exceeded.
+                    if wrap_lines and x + char_width > width:
+                        visible_line_to_row_col[y + 1] = (
+                            lineno,
+                            visible_line_to_row_col[y][1] + x,
+                        )
+                        y += 1
+                        wrap_count += 1
+                        x = 0
+
+                        # Insert line prefix (continuation prompt).
+                        if is_input and get_line_prefix:
+                            prompt = to_formatted_text(
+                                get_line_prefix(lineno, wrap_count)
+                            )
+                            x, y = copy_line(prompt, lineno, x, y, is_input=False)
+
+                        new_buffer_row = new_buffer[y + ypos]
+
+                        if y >= write_position.height:
+                            return x, y  # Break out of all for loops.
+
+                    # Set character in screen and shift 'x'.
+                    if x >= 0 and y >= 0 and x < width:
+                        new_buffer_row[x + xpos] = char
+
+                        # When we print a multi width character, make sure
+                        # to erase the neighbours positions in the screen.
+                        # (The empty string if different from everything,
+                        # so next redraw this cell will repaint anyway.)
+                        if char_width > 1:
+                            for i in range(1, char_width):
+                                new_buffer_row[x + xpos + i] = empty_char
+
+                        # If this is a zero width characters, then it's
+                        # probably part of a decomposed unicode character.
+                        # See: https://en.wikipedia.org/wiki/Unicode_equivalence
+                        # Merge it in the previous cell.
+                        elif char_width == 0:
+                            # Handle all character widths. If the previous
+                            # character is a multiwidth character, then
+                            # merge it two positions back.
+                            for pw in [2, 1]:  # Previous character width.
+                                if (
+                                    x - pw >= 0
+                                    and new_buffer_row[x + xpos - pw].width == pw
+                                ):
+                                    prev_char = new_buffer_row[x + xpos - pw]
+                                    char2 = _CHAR_CACHE[
+                                        prev_char.char + c, prev_char.style
+                                    ]
+                                    new_buffer_row[x + xpos - pw] = char2
+
+                        # Keep track of write position for each character.
+                        current_rowcol_to_yx[lineno, col + skipped] = (
+                            y + ypos,
+                            x + xpos,
+                        )
+
+                    col += 1
+                    x += char_width
+            return x, y
+
+        # Copy content.
+        def copy() -> int:
+            y = -vertical_scroll_2
+            lineno = vertical_scroll
+
+            while y < write_position.height and lineno < line_count:
+                # Take the next line and copy it in the real screen.
+                line = ui_content.get_line(lineno)
+
+                visible_line_to_row_col[y] = (lineno, horizontal_scroll)
+
+                # Copy margin and actual line.
+                x = 0
+                x, y = copy_line(line, lineno, x, y, is_input=True)
+
+                lineno += 1
+                y += 1
+            return y
+
+        copy()
+
+        def cursor_pos_to_screen_pos(row: int, col: int) -> Point:
+            "Translate row/col from UIContent to real Screen coordinates."
+            try:
+                y, x = rowcol_to_yx[row, col]
+            except KeyError:
+                # Normally this should never happen. (It is a bug, if it happens.)
+                # But to be sure, return (0, 0)
+                return Point(x=0, y=0)
+
+                # raise ValueError(
+                #     'Invalid position. row=%r col=%r, vertical_scroll=%r, '
+                #     'horizontal_scroll=%r, height=%r' %
+                #     (row, col, vertical_scroll, horizontal_scroll, write_position.height))
+            else:
+                return Point(x=x, y=y)
+
+        # Set cursor and menu positions.
+        if ui_content.cursor_position:
+            screen_cursor_position = cursor_pos_to_screen_pos(
+                ui_content.cursor_position.y, ui_content.cursor_position.x
+            )
+
+            if has_focus:
+                new_screen.set_cursor_position(self, screen_cursor_position)
+
+                if always_hide_cursor:
+                    new_screen.show_cursor = False
+                else:
+                    new_screen.show_cursor = ui_content.show_cursor
+
+                self._highlight_digraph(new_screen)
+
+            if highlight_lines:
+                self._highlight_cursorlines(
+                    new_screen,
+                    screen_cursor_position,
+                    xpos,
+                    ypos,
+                    width,
+                    write_position.height,
+                )
+
+        # Draw input characters from the input processor queue.
+        if has_focus and ui_content.cursor_position:
+            self._show_key_processor_key_buffer(new_screen)
+
+        # Set menu position.
+        if ui_content.menu_position:
+            new_screen.set_menu_position(
+                self,
+                cursor_pos_to_screen_pos(
+                    ui_content.menu_position.y, ui_content.menu_position.x
+                ),
+            )
+
+        # Update output screen height.
+        new_screen.height = max(new_screen.height, ypos + write_position.height)
+
+        return visible_line_to_row_col, rowcol_to_yx
+
+    def _fill_bg(
+        self, screen: Screen, write_position: WritePosition, erase_bg: bool
+    ) -> None:
+        """
+        Erase/fill the background.
+        (Useful for floats and when a `char` has been given.)
+        """
+        char: Optional[str]
+        if callable(self.char):
+            char = self.char()
+        else:
+            char = self.char
+
+        if erase_bg or char:
+            wp = write_position
+            char_obj = _CHAR_CACHE[char or " ", ""]
+
+            for y in range(wp.ypos, wp.ypos + wp.height):
+                row = screen.data_buffer[y]
+                for x in range(wp.xpos, wp.xpos + wp.width):
+                    row[x] = char_obj
+
+    def _apply_style(
+        self, new_screen: Screen, write_position: WritePosition, parent_style: str
+    ) -> None:
+
+        # Apply `self.style`.
+        style = parent_style + " " + to_str(self.style)
+
+        new_screen.fill_area(write_position, style=style, after=False)
+
+        # Apply the 'last-line' class to the last line of each Window. This can
+        # be used to apply an 'underline' to the user control.
+        wp = WritePosition(
+            write_position.xpos,
+            write_position.ypos + write_position.height - 1,
+            write_position.width,
+            1,
+        )
+        new_screen.fill_area(wp, "class:last-line", after=True)
+
+    def _highlight_digraph(self, new_screen: Screen) -> None:
+        """
+        When we are in Vi digraph mode, put a question mark underneath the
+        cursor.
+        """
+        digraph_char = self._get_digraph_char()
+        if digraph_char:
+            cpos = new_screen.get_cursor_position(self)
+            new_screen.data_buffer[cpos.y][cpos.x] = _CHAR_CACHE[
+                digraph_char, "class:digraph"
+            ]
+
+    def _show_key_processor_key_buffer(self, new_screen: Screen) -> None:
+        """
+        When the user is typing a key binding that consists of several keys,
+        display the last pressed key if the user is in insert mode and the key
+        is meaningful to be displayed.
+        E.g. Some people want to bind 'jj' to escape in Vi insert mode. But the
+             first 'j' needs to be displayed in order to get some feedback.
+        """
+        app = get_app()
+        key_buffer = app.key_processor.key_buffer
+
+        if key_buffer and _in_insert_mode() and not app.is_done:
+            # The textual data for the given key. (Can be a VT100 escape
+            # sequence.)
+            data = key_buffer[-1].data
+
+            # Display only if this is a 1 cell width character.
+            if get_cwidth(data) == 1:
+                cpos = new_screen.get_cursor_position(self)
+                new_screen.data_buffer[cpos.y][cpos.x] = _CHAR_CACHE[
+                    data, "class:partial-key-binding"
+                ]
+
+    def _highlight_cursorlines(
+        self, new_screen: Screen, cpos: Point, x: int, y: int, width: int, height: int
+    ) -> None:
+        """
+        Highlight cursor row/column.
+        """
+        cursor_line_style = " class:cursor-line "
+        cursor_column_style = " class:cursor-column "
+
+        data_buffer = new_screen.data_buffer
+
+        # Highlight cursor line.
+        if self.cursorline():
+            row = data_buffer[cpos.y]
+            for x in range(x, x + width):
+                original_char = row[x]
+                row[x] = _CHAR_CACHE[
+                    original_char.char, original_char.style + cursor_line_style
+                ]
+
+        # Highlight cursor column.
+        if self.cursorcolumn():
+            for y2 in range(y, y + height):
+                row = data_buffer[y2]
+                original_char = row[cpos.x]
+                row[cpos.x] = _CHAR_CACHE[
+                    original_char.char, original_char.style + cursor_column_style
+                ]
+
+        # Highlight color columns
+        colorcolumns = self.colorcolumns
+        if callable(colorcolumns):
+            colorcolumns = colorcolumns()
+
+        for cc in colorcolumns:
+            assert isinstance(cc, ColorColumn)
+            column = cc.position
+
+            if column < x + width:  # Only draw when visible.
+                color_column_style = " " + cc.style
+
+                for y2 in range(y, y + height):
+                    row = data_buffer[y2]
+                    original_char = row[column + x]
+                    row[column + x] = _CHAR_CACHE[
+                        original_char.char, original_char.style + color_column_style
+                    ]
+
+    def _copy_margin(
+        self,
+        margin_content: UIContent,
+        new_screen: Screen,
+        write_position: WritePosition,
+        move_x: int,
+        width: int,
+    ) -> None:
+        """
+        Copy characters from the margin screen to the real screen.
+        """
+        xpos = write_position.xpos + move_x
+        ypos = write_position.ypos
+
+        margin_write_position = WritePosition(xpos, ypos, width, write_position.height)
+        self._copy_body(margin_content, new_screen, margin_write_position, 0, width)
+
+    def _scroll(self, ui_content: UIContent, width: int, height: int) -> None:
+        """
+        Scroll body. Ensure that the cursor is visible.
+        """
+        if self.wrap_lines():
+            func = self._scroll_when_linewrapping
+        else:
+            func = self._scroll_without_linewrapping
+
+        func(ui_content, width, height)
+
+    def _scroll_when_linewrapping(
+        self, ui_content: UIContent, width: int, height: int
+    ) -> None:
+        """
+        Scroll to make sure the cursor position is visible and that we maintain
+        the requested scroll offset.
+
+        Set `self.horizontal_scroll/vertical_scroll`.
+        """
+        scroll_offsets_bottom = self.scroll_offsets.bottom
+        scroll_offsets_top = self.scroll_offsets.top
+
+        # We don't have horizontal scrolling.
+        self.horizontal_scroll = 0
+
+        def get_line_height(lineno: int) -> int:
+            return ui_content.get_height_for_line(lineno, width, self.get_line_prefix)
+
+        # When there is no space, reset `vertical_scroll_2` to zero and abort.
+        # This can happen if the margin is bigger than the window width.
+        # Otherwise the text height will become "infinite" (a big number) and
+        # the copy_line will spend a huge amount of iterations trying to render
+        # nothing.
+        if width <= 0:
+            self.vertical_scroll = ui_content.cursor_position.y
+            self.vertical_scroll_2 = 0
+            return
+
+        # If the current line consumes more than the whole window height,
+        # then we have to scroll vertically inside this line. (We don't take
+        # the scroll offsets into account for this.)
+        # Also, ignore the scroll offsets in this case. Just set the vertical
+        # scroll to this line.
+        line_height = get_line_height(ui_content.cursor_position.y)
+        if line_height > height - scroll_offsets_top:
+            # Calculate the height of the text before the cursor (including
+            # line prefixes).
+            text_before_height = ui_content.get_height_for_line(
+                ui_content.cursor_position.y,
+                width,
+                self.get_line_prefix,
+                slice_stop=ui_content.cursor_position.x,
+            )
+
+            # Adjust scroll offset.
+            self.vertical_scroll = ui_content.cursor_position.y
+            self.vertical_scroll_2 = min(
+                text_before_height - 1,  # Keep the cursor visible.
+                line_height
+                - height,  # Avoid blank lines at the bottom when scolling up again.
+                self.vertical_scroll_2,
+            )
+            self.vertical_scroll_2 = max(
+                0, text_before_height - height, self.vertical_scroll_2
+            )
+            return
+        else:
+            self.vertical_scroll_2 = 0
+
+        # Current line doesn't consume the whole height. Take scroll offsets into account.
+        def get_min_vertical_scroll() -> int:
+            # Make sure that the cursor line is not below the bottom.
+            # (Calculate how many lines can be shown between the cursor and the .)
+            used_height = 0
+            prev_lineno = ui_content.cursor_position.y
+
+            for lineno in range(ui_content.cursor_position.y, -1, -1):
+                used_height += get_line_height(lineno)
+
+                if used_height > height - scroll_offsets_bottom:
+                    return prev_lineno
+                else:
+                    prev_lineno = lineno
+            return 0
+
+        def get_max_vertical_scroll() -> int:
+            # Make sure that the cursor line is not above the top.
+            prev_lineno = ui_content.cursor_position.y
+            used_height = 0
+
+            for lineno in range(ui_content.cursor_position.y - 1, -1, -1):
+                used_height += get_line_height(lineno)
+
+                if used_height > scroll_offsets_top:
+                    return prev_lineno
+                else:
+                    prev_lineno = lineno
+            return prev_lineno
+
+        def get_topmost_visible() -> int:
+            """
+            Calculate the upper most line that can be visible, while the bottom
+            is still visible. We should not allow scroll more than this if
+            `allow_scroll_beyond_bottom` is false.
+            """
+            prev_lineno = ui_content.line_count - 1
+            used_height = 0
+            for lineno in range(ui_content.line_count - 1, -1, -1):
+                used_height += get_line_height(lineno)
+                if used_height > height:
+                    return prev_lineno
+                else:
+                    prev_lineno = lineno
+            return prev_lineno
+
+        # Scroll vertically. (Make sure that the whole line which contains the
+        # cursor is visible.
+        topmost_visible = get_topmost_visible()
+
+        # Note: the `min(topmost_visible, ...)` is to make sure that we
+        # don't require scrolling up because of the bottom scroll offset,
+        # when we are at the end of the document.
+        self.vertical_scroll = max(
+            self.vertical_scroll, min(topmost_visible, get_min_vertical_scroll())
+        )
+        self.vertical_scroll = min(self.vertical_scroll, get_max_vertical_scroll())
+
+        # Disallow scrolling beyond bottom?
+        if not self.allow_scroll_beyond_bottom():
+            self.vertical_scroll = min(self.vertical_scroll, topmost_visible)
+
+    def _scroll_without_linewrapping(
+        self, ui_content: UIContent, width: int, height: int
+    ) -> None:
+        """
+        Scroll to make sure the cursor position is visible and that we maintain
+        the requested scroll offset.
+
+        Set `self.horizontal_scroll/vertical_scroll`.
+        """
+        cursor_position = ui_content.cursor_position or Point(x=0, y=0)
+
+        # Without line wrapping, we will never have to scroll vertically inside
+        # a single line.
+        self.vertical_scroll_2 = 0
+
+        if ui_content.line_count == 0:
+            self.vertical_scroll = 0
+            self.horizontal_scroll = 0
+            return
+        else:
+            current_line_text = fragment_list_to_text(
+                ui_content.get_line(cursor_position.y)
+            )
+
+        def do_scroll(
+            current_scroll: int,
+            scroll_offset_start: int,
+            scroll_offset_end: int,
+            cursor_pos: int,
+            window_size: int,
+            content_size: int,
+        ) -> int:
+            "Scrolling algorithm. Used for both horizontal and vertical scrolling."
+            # Calculate the scroll offset to apply.
+            # This can obviously never be more than have the screen size. Also, when the
+            # cursor appears at the top or bottom, we don't apply the offset.
+            scroll_offset_start = int(
+                min(scroll_offset_start, window_size / 2, cursor_pos)
+            )
+            scroll_offset_end = int(
+                min(scroll_offset_end, window_size / 2, content_size - 1 - cursor_pos)
+            )
+
+            # Prevent negative scroll offsets.
+            if current_scroll < 0:
+                current_scroll = 0
+
+            # Scroll back if we scrolled to much and there's still space to show more of the document.
+            if (
+                not self.allow_scroll_beyond_bottom()
+                and current_scroll > content_size - window_size
+            ):
+                current_scroll = max(0, content_size - window_size)
+
+            # Scroll up if cursor is before visible part.
+            if current_scroll > cursor_pos - scroll_offset_start:
+                current_scroll = max(0, cursor_pos - scroll_offset_start)
+
+            # Scroll down if cursor is after visible part.
+            if current_scroll < (cursor_pos + 1) - window_size + scroll_offset_end:
+                current_scroll = (cursor_pos + 1) - window_size + scroll_offset_end
+
+            return current_scroll
+
+        # When a preferred scroll is given, take that first into account.
+        if self.get_vertical_scroll:
+            self.vertical_scroll = self.get_vertical_scroll(self)
+            assert isinstance(self.vertical_scroll, int)
+        if self.get_horizontal_scroll:
+            self.horizontal_scroll = self.get_horizontal_scroll(self)
+            assert isinstance(self.horizontal_scroll, int)
+
+        # Update horizontal/vertical scroll to make sure that the cursor
+        # remains visible.
+        offsets = self.scroll_offsets
+
+        self.vertical_scroll = do_scroll(
+            current_scroll=self.vertical_scroll,
+            scroll_offset_start=offsets.top,
+            scroll_offset_end=offsets.bottom,
+            cursor_pos=ui_content.cursor_position.y,
+            window_size=height,
+            content_size=ui_content.line_count,
+        )
+
+        if self.get_line_prefix:
+            current_line_prefix_width = fragment_list_width(
+                to_formatted_text(self.get_line_prefix(ui_content.cursor_position.y, 0))
+            )
+        else:
+            current_line_prefix_width = 0
+
+        self.horizontal_scroll = do_scroll(
+            current_scroll=self.horizontal_scroll,
+            scroll_offset_start=offsets.left,
+            scroll_offset_end=offsets.right,
+            cursor_pos=get_cwidth(current_line_text[: ui_content.cursor_position.x]),
+            window_size=width - current_line_prefix_width,
+            # We can only analyse the current line. Calculating the width off
+            # all the lines is too expensive.
+            content_size=max(
+                get_cwidth(current_line_text), self.horizontal_scroll + width
+            ),
+        )
+
+    def _mouse_handler(self, mouse_event: MouseEvent) -> "NotImplementedOrNone":
+        """
+        Mouse handler. Called when the UI control doesn't handle this
+        particular event.
+
+        Return `NotImplemented` if nothing was done as a consequence of this
+        key binding (no UI invalidate required in that case).
+        """
+        if mouse_event.event_type == MouseEventType.SCROLL_DOWN:
+            self._scroll_down()
+            return None
+        elif mouse_event.event_type == MouseEventType.SCROLL_UP:
+            self._scroll_up()
+            return None
+
+        return NotImplemented
+
+    def _scroll_down(self) -> None:
+        "Scroll window down."
+        info = self.render_info
+
+        if info is None:
+            return
+
+        if self.vertical_scroll < info.content_height - info.window_height:
+            if info.cursor_position.y <= info.configured_scroll_offsets.top:
+                self.content.move_cursor_down()
+
+            self.vertical_scroll += 1
+
+    def _scroll_up(self) -> None:
+        "Scroll window up."
+        info = self.render_info
+
+        if info is None:
+            return
+
+        if info.vertical_scroll > 0:
+            # TODO: not entirely correct yet in case of line wrapping and long lines.
+            if (
+                info.cursor_position.y
+                >= info.window_height - 1 - info.configured_scroll_offsets.bottom
+            ):
+                self.content.move_cursor_up()
+
+            self.vertical_scroll -= 1
+
+    def get_key_bindings(self) -> Optional[KeyBindingsBase]:
+        return self.content.get_key_bindings()
+
+    def get_children(self) -> List[Container]:
+        return []
+
+
+class ConditionalContainer(Container):
+    """
+    Wrapper around any other container that can change the visibility. The
+    received `filter` determines whether the given container should be
+    displayed or not.
+
+    :param content: :class:`.Container` instance.
+    :param filter: :class:`.Filter` instance.
+    """
+
+    def __init__(self, content: AnyContainer, filter: FilterOrBool) -> None:
+        self.content = to_container(content)
+        self.filter = to_filter(filter)
+
+    def __repr__(self) -> str:
+        return f"ConditionalContainer({self.content!r}, filter={self.filter!r})"
+
+    def reset(self) -> None:
+        self.content.reset()
+
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        if self.filter():
+            return self.content.preferred_width(max_available_width)
+        else:
+            return Dimension.zero()
+
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        if self.filter():
+            return self.content.preferred_height(width, max_available_height)
+        else:
+            return Dimension.zero()
+
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        if self.filter():
+            return self.content.write_to_screen(
+                screen, mouse_handlers, write_position, parent_style, erase_bg, z_index
+            )
+
+    def get_children(self) -> List[Container]:
+        return [self.content]
+
+
+class DynamicContainer(Container):
+    """
+    Container class that dynamically returns any Container.
+
+    :param get_container: Callable that returns a :class:`.Container` instance
+        or any widget with a ``__pt_container__`` method.
+    """
+
+    def __init__(self, get_container: Callable[[], AnyContainer]) -> None:
+        self.get_container = get_container
+
+    def _get_container(self) -> Container:
+        """
+        Return the current container object.
+
+        We call `to_container`, because `get_container` can also return a
+        widget with a ``__pt_container__`` method.
+        """
+        obj = self.get_container()
+        return to_container(obj)
+
+    def reset(self) -> None:
+        self._get_container().reset()
+
+    def preferred_width(self, max_available_width: int) -> Dimension:
+        return self._get_container().preferred_width(max_available_width)
+
+    def preferred_height(self, width: int, max_available_height: int) -> Dimension:
+        return self._get_container().preferred_height(width, max_available_height)
+
+    def write_to_screen(
+        self,
+        screen: Screen,
+        mouse_handlers: MouseHandlers,
+        write_position: WritePosition,
+        parent_style: str,
+        erase_bg: bool,
+        z_index: Optional[int],
+    ) -> None:
+        self._get_container().write_to_screen(
+            screen, mouse_handlers, write_position, parent_style, erase_bg, z_index
+        )
+
+    def is_modal(self) -> bool:
+        return False
+
+    def get_key_bindings(self) -> Optional[KeyBindingsBase]:
+        # Key bindings will be collected when `layout.walk()` finds the child
+        # container.
+        return None
+
+    def get_children(self) -> List[Container]:
+        # Here we have to return the current active container itself, not its
+        # children. Otherwise, we run into issues where `layout.walk()` will
+        # never see an object of type `Window` if this contains a window. We
+        # can't/shouldn't proxy the "isinstance" check.
+        return [self._get_container()]
+
+
+def to_container(container: AnyContainer) -> Container:
+    """
+    Make sure that the given object is a :class:`.Container`.
+    """
+    if isinstance(container, Container):
+        return container
+    elif hasattr(container, "__pt_container__"):
+        return to_container(container.__pt_container__())
+    else:
+        raise ValueError(f"Not a container object: {container!r}")
+
+
+def to_window(container: AnyContainer) -> Window:
+    """
+    Make sure that the given argument is a :class:`.Window`.
+    """
+    if isinstance(container, Window):
+        return container
+    elif hasattr(container, "__pt_container__"):
+        return to_window(cast("MagicContainer", container).__pt_container__())
+    else:
+        raise ValueError(f"Not a Window object: {container!r}.")
+
+
+def is_container(value: object) -> "TypeGuard[AnyContainer]":
+    """
+    Checks whether the given value is a container object
+    (for use in assert statements).
+    """
+    if isinstance(value, Container):
+        return True
+    if hasattr(value, "__pt_container__"):
+        return is_container(cast("MagicContainer", value).__pt_container__())
+    return False