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diff --git a/src/prompt_toolkit/styles/base.py b/src/prompt_toolkit/styles/base.py
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+++ b/src/prompt_toolkit/styles/base.py
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+"""
+The base classes for the styling.
+"""
+from __future__ import annotations
+
+from abc import ABCMeta, abstractmethod, abstractproperty
+from typing import Callable, Hashable, NamedTuple
+
+__all__ = [
+    "Attrs",
+    "DEFAULT_ATTRS",
+    "ANSI_COLOR_NAMES",
+    "ANSI_COLOR_NAMES_ALIASES",
+    "BaseStyle",
+    "DummyStyle",
+    "DynamicStyle",
+]
+
+
+#: Style attributes.
+class Attrs(NamedTuple):
+    color: str | None
+    bgcolor: str | None
+    bold: bool | None
+    underline: bool | None
+    strike: bool | None
+    italic: bool | None
+    blink: bool | None
+    reverse: bool | None
+    hidden: bool | None
+
+
+"""
+:param color: Hexadecimal string. E.g. '000000' or Ansi color name: e.g. 'ansiblue'
+:param bgcolor: Hexadecimal string. E.g. 'ffffff' or Ansi color name: e.g. 'ansired'
+:param bold: Boolean
+:param underline: Boolean
+:param strike: Boolean
+:param italic: Boolean
+:param blink: Boolean
+:param reverse: Boolean
+:param hidden: Boolean
+"""
+
+#: The default `Attrs`.
+DEFAULT_ATTRS = Attrs(
+    color="",
+    bgcolor="",
+    bold=False,
+    underline=False,
+    strike=False,
+    italic=False,
+    blink=False,
+    reverse=False,
+    hidden=False,
+)
+
+
+#: ``Attrs.bgcolor/fgcolor`` can be in either 'ffffff' format, or can be any of
+#: the following in case we want to take colors from the 8/16 color palette.
+#: Usually, in that case, the terminal application allows to configure the RGB
+#: values for these names.
+#: ISO 6429 colors
+ANSI_COLOR_NAMES = [
+    "ansidefault",
+    # Low intensity, dark.  (One or two components 0x80, the other 0x00.)
+    "ansiblack",
+    "ansired",
+    "ansigreen",
+    "ansiyellow",
+    "ansiblue",
+    "ansimagenta",
+    "ansicyan",
+    "ansigray",
+    # High intensity, bright. (One or two components 0xff, the other 0x00. Not supported everywhere.)
+    "ansibrightblack",
+    "ansibrightred",
+    "ansibrightgreen",
+    "ansibrightyellow",
+    "ansibrightblue",
+    "ansibrightmagenta",
+    "ansibrightcyan",
+    "ansiwhite",
+]
+
+
+# People don't use the same ANSI color names everywhere. In prompt_toolkit 1.0
+# we used some unconventional names (which were contributed like that to
+# Pygments). This is fixed now, but we still support the old names.
+
+# The table below maps the old aliases to the current names.
+ANSI_COLOR_NAMES_ALIASES: dict[str, str] = {
+    "ansidarkgray": "ansibrightblack",
+    "ansiteal": "ansicyan",
+    "ansiturquoise": "ansibrightcyan",
+    "ansibrown": "ansiyellow",
+    "ansipurple": "ansimagenta",
+    "ansifuchsia": "ansibrightmagenta",
+    "ansilightgray": "ansigray",
+    "ansidarkred": "ansired",
+    "ansidarkgreen": "ansigreen",
+    "ansidarkblue": "ansiblue",
+}
+assert set(ANSI_COLOR_NAMES_ALIASES.values()).issubset(set(ANSI_COLOR_NAMES))
+assert not (set(ANSI_COLOR_NAMES_ALIASES.keys()) & set(ANSI_COLOR_NAMES))
+
+
+class BaseStyle(metaclass=ABCMeta):
+    """
+    Abstract base class for prompt_toolkit styles.
+    """
+
+    @abstractmethod
+    def get_attrs_for_style_str(
+        self, style_str: str, default: Attrs = DEFAULT_ATTRS
+    ) -> Attrs:
+        """
+        Return :class:`.Attrs` for the given style string.
+
+        :param style_str: The style string. This can contain inline styling as
+            well as classnames (e.g. "class:title").
+        :param default: `Attrs` to be used if no styling was defined.
+        """
+
+    @abstractproperty
+    def style_rules(self) -> list[tuple[str, str]]:
+        """
+        The list of style rules, used to create this style.
+        (Required for `DynamicStyle` and `_MergedStyle` to work.)
+        """
+        return []
+
+    @abstractmethod
+    def invalidation_hash(self) -> Hashable:
+        """
+        Invalidation hash for the style. When this changes over time, the
+        renderer knows that something in the style changed, and that everything
+        has to be redrawn.
+        """
+
+
+class DummyStyle(BaseStyle):
+    """
+    A style that doesn't style anything.
+    """
+
+    def get_attrs_for_style_str(
+        self, style_str: str, default: Attrs = DEFAULT_ATTRS
+    ) -> Attrs:
+        return default
+
+    def invalidation_hash(self) -> Hashable:
+        return 1  # Always the same value.
+
+    @property
+    def style_rules(self) -> list[tuple[str, str]]:
+        return []
+
+
+class DynamicStyle(BaseStyle):
+    """
+    Style class that can dynamically returns an other Style.
+
+    :param get_style: Callable that returns a :class:`.Style` instance.
+    """
+
+    def __init__(self, get_style: Callable[[], BaseStyle | None]):
+        self.get_style = get_style
+        self._dummy = DummyStyle()
+
+    def get_attrs_for_style_str(
+        self, style_str: str, default: Attrs = DEFAULT_ATTRS
+    ) -> Attrs:
+        style = self.get_style() or self._dummy
+
+        return style.get_attrs_for_style_str(style_str, default)
+
+    def invalidation_hash(self) -> Hashable:
+        return (self.get_style() or self._dummy).invalidation_hash()
+
+    @property
+    def style_rules(self) -> list[tuple[str, str]]:
+        return (self.get_style() or self._dummy).style_rules