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

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+*usr_28.txt*	For Vim version 8.1.  Last change: 2008 Jun 14
+
+		     VIM USER MANUAL - by Bram Moolenaar
+
+				   Folding
+
+
+Structured text can be separated in sections.  And sections in sub-sections.
+Folding allows you to display a section as one line, providing an overview.
+This chapter explains the different ways this can be done.
+
+|28.1|	What is folding?
+|28.2|	Manual folding
+|28.3|	Working with folds
+|28.4|	Saving and restoring folds
+|28.5|	Folding by indent
+|28.6|	Folding with markers
+|28.7|	Folding by syntax
+|28.8|	Folding by expression
+|28.9|	Folding unchanged lines
+|28.10|	Which fold method to use?
+
+     Next chapter: |usr_29.txt|  Moving through programs
+ Previous chapter: |usr_27.txt|  Search commands and patterns
+Table of contents: |usr_toc.txt|
+
+==============================================================================
+*28.1*	What is folding?
+
+Folding is used to show a range of lines in the buffer as a single line on the
+screen.  Like a piece of paper which is folded to make it shorter:
+
+	+------------------------+
+	| line 1		 |
+	| line 2		 |
+	| line 3		 |
+	|_______________________ |
+	\			 \
+	 \________________________\
+	 / folded lines		  /
+	/________________________/
+	| line 12		 |
+	| line 13		 |
+	| line 14		 |
+	+------------------------+
+
+The text is still in the buffer, unchanged.  Only the way lines are displayed
+is affected by folding.
+
+The advantage of folding is that you can get a better overview of the
+structure of text, by folding lines of a section and replacing it with a line
+that indicates that there is a section.
+
+==============================================================================
+*28.2*	Manual folding
+
+Try it out: Position the cursor in a paragraph and type: >
+
+	zfap
+
+You will see that the paragraph is replaced by a highlighted line.  You have
+created a fold.  |zf| is an operator and |ap| a text object selection.  You
+can use the |zf| operator with any movement command to create a fold for the
+text that it moved over.  |zf| also works in Visual mode.
+
+To view the text again, open the fold by typing: >
+
+	zo
+
+And you can close the fold again with: >
+
+	zc
+
+All the folding commands start with "z".  With some fantasy, this looks like a
+folded piece of paper, seen from the side.  The letter after the "z" has a
+mnemonic meaning to make it easier to remember the commands:
+
+	zf	F-old creation
+	zo	O-pen a fold
+	zc	C-lose a fold
+
+Folds can be nested: A region of text that contains folds can be folded
+again.  For example, you can fold each paragraph in this section, and then
+fold all the sections in this chapter.  Try it out.  You will notice that
+opening the fold for the whole chapter will restore the nested folds as they
+were, some may be open and some may be closed.
+
+Suppose you have created several folds, and now want to view all the text.
+You could go to each fold and type "zo".  To do this faster, use this command: >
+
+	zr
+
+This will R-educe the folding.  The opposite is: >
+
+	zm
+
+This folds M-ore.  You can repeat "zr" and "zm" to open and close nested folds
+of several levels.
+
+If you have nested several levels deep, you can open all of them with: >
+
+	zR
+
+This R-educes folds until there are none left.  And you can close all folds
+with: >
+
+	zM
+
+This folds M-ore and M-ore.
+
+You can quickly disable the folding with the |zn| command.  Then |zN| brings
+back the folding as it was.  |zi| toggles between the two.  This is a useful
+way of working:
+- create folds to get overview on your file
+- move around to where you want to do your work
+- do |zi| to look at the text and edit it
+- do |zi| again to go back to moving around
+
+More about manual folding in the reference manual: |fold-manual|
+
+==============================================================================
+*28.3*	Working with folds
+
+When some folds are closed, movement commands like "j" and "k" move over a
+fold like it was a single, empty line.  This allows you to quickly move around
+over folded text.
+
+You can yank, delete and put folds as if it was a single line.  This is very
+useful if you want to reorder functions in a program.  First make sure that
+each fold contains a whole function (or a bit less) by selecting the right
+'foldmethod'.  Then delete the function with "dd", move the cursor and put it
+with "p".  If some lines of the function are above or below the fold, you can
+use Visual selection:
+- put the cursor on the first line to be moved
+- hit "V" to start Visual mode
+- put the cursor on the last line to be moved
+- hit "d" to delete the selected lines.
+- move the cursor to the new position and "p"ut the lines there.
+
+It is sometimes difficult to see or remember where a fold is located, thus
+where a |zo| command would actually work.  To see the defined folds: >
+
+	:set foldcolumn=4
+
+This will show a small column on the left of the window to indicate folds.
+A "+" is shown for a closed fold.  A "-" is shown at the start of each open
+fold and "|" at following lines of the fold.
+
+You can use the mouse to open a fold by clicking on the "+" in the foldcolumn.
+Clicking on the "-" or a "|" below it will close an open fold.
+
+To open all folds at the cursor line use |zO|.
+To close all folds at the cursor line use |zC|.
+To delete a fold at the cursor line use |zd|.
+To delete all folds at the cursor line use |zD|.
+
+When in Insert mode, the fold at the cursor line is never closed.  That allows
+you to see what you type!
+
+Folds are opened automatically when jumping around or moving the cursor left
+or right.  For example, the "0" command opens the fold under the cursor
+(if 'foldopen' contains "hor", which is the default).  The 'foldopen' option
+can be changed to open folds for specific commands.  If you want the line
+under the cursor always to be open, do this: >
+
+	:set foldopen=all
+
+Warning: You won't be able to move onto a closed fold then.  You might want to
+use this only temporarily and then set it back to the default: >
+
+	:set foldopen&
+
+You can make folds close automatically when you move out of it: >
+
+	:set foldclose=all
+
+This will re-apply 'foldlevel' to all folds that don't contain the cursor.
+You have to try it out if you like how this feels.  Use |zm| to fold more and
+|zr| to fold less (reduce folds).
+
+The folding is local to the window.  This allows you to open two windows on
+the same buffer, one with folds and one without folds.  Or one with all folds
+closed and one with all folds open.
+
+==============================================================================
+*28.4*	Saving and restoring folds
+
+When you abandon a file (starting to edit another one), the state of the folds
+is lost.  If you come back to the same file later, all manually opened and
+closed folds are back to their default.  When folds have been created
+manually, all folds are gone!  To save the folds use the |:mkview| command: >
+
+	:mkview
+
+This will store the settings and other things that influence the view on the
+file.  You can change what is stored with the 'viewoptions' option.
+When you come back to the same file later, you can load the view again: >
+
+	:loadview
+
+You can store up to ten views on one file.  For example, to save the current
+setup as the third view and load the second view: >
+
+	:mkview 3
+	:loadview 2
+
+Note that when you insert or delete lines the views might become invalid.
+Also check out the 'viewdir' option, which specifies where the views are
+stored.  You might want to delete old views now and then.
+
+==============================================================================
+*28.5*	Folding by indent
+
+Defining folds with |zf| is a lot of work.  If your text is structured by
+giving lower level items a larger indent, you can use the indent folding
+method.  This will create folds for every sequence of lines with the same
+indent.  Lines with a larger indent will become nested folds.  This works well
+with many programming languages.
+
+Try this by setting the 'foldmethod' option: >
+
+	:set foldmethod=indent
+
+Then you can use the |zm| and |zr| commands to fold more and reduce folding.
+It's easy to see on this example text:
+
+This line is not indented
+	This line is indented once
+		This line is indented twice
+		This line is indented twice
+	This line is indented once
+This line is not indented
+	This line is indented once
+	This line is indented once
+
+Note that the relation between the amount of indent and the fold depth depends
+on the 'shiftwidth' option.  Each 'shiftwidth' worth of indent adds one to the
+depth of the fold.  This is called a fold level.
+
+When you use the |zr| and |zm| commands you actually increase or decrease the
+'foldlevel' option.  You could also set it directly: >
+
+	:set foldlevel=3
+
+This means that all folds with three times a 'shiftwidth' indent or more will
+be closed.  The lower the foldlevel, the more folds will be closed.  When
+'foldlevel' is zero, all folds are closed.  |zM| does set 'foldlevel' to zero.
+The opposite command |zR| sets 'foldlevel' to the deepest fold level that is
+present in the file.
+
+Thus there are two ways to open and close the folds:
+(A) By setting the fold level.
+    This gives a very quick way of "zooming out" to view the structure of the
+    text, move the cursor, and "zoom in" on the text again.
+
+(B) By using |zo| and |zc| commands to open or close specific folds.
+    This allows opening only those folds that you want to be open, while other
+    folds remain closed.
+
+This can be combined: You can first close most folds by using |zm| a few times
+and then open a specific fold with |zo|.  Or open all folds with |zR| and
+then close specific folds with |zc|.
+
+But you cannot manually define folds when 'foldmethod' is "indent", as that
+would conflict with the relation between the indent and the fold level.
+
+More about folding by indent in the reference manual: |fold-indent|
+
+==============================================================================
+*28.6*	Folding with markers
+
+Markers in the text are used to specify the start and end of a fold region.
+This gives precise control over which lines are included in a fold.  The
+disadvantage is that the text needs to be modified.
+
+Try it: >
+
+	:set foldmethod=marker
+
+Example text, as it could appear in a C program:
+
+	/* foobar () {{{ */
+	int foobar()
+	{
+		/* return a value {{{ */
+		return 42;
+		/* }}} */
+	}
+	/* }}} */
+
+Notice that the folded line will display the text before the marker.  This is
+very useful to tell what the fold contains.
+
+It's quite annoying when the markers don't pair up correctly after moving some
+lines around.  This can be avoided by using numbered markers.  Example:
+
+	/* global variables {{{1 */
+	int varA, varB;
+
+	/* functions {{{1 */
+	/* funcA() {{{2 */
+	void funcA() {}
+
+	/* funcB() {{{2 */
+	void funcB() {}
+	/* }}}1 */
+
+At every numbered marker a fold at the specified level begins.  This will make
+any fold at a higher level stop here.  You can just use numbered start markers
+to define all folds.  Only when you want to explicitly stop a fold before
+another starts you need to add an end marker.
+
+More about folding with markers in the reference manual: |fold-marker|
+
+==============================================================================
+*28.7*	Folding by syntax
+
+For each language Vim uses a different syntax file.  This defines the colors
+for various items in the file.  If you are reading this in Vim, in a terminal
+that supports colors, the colors you see are made with the "help" syntax file.
+   In the syntax files it is possible to add syntax items that have the "fold"
+argument.  These define a fold region.  This requires writing a syntax file
+and adding these items in it.  That's not so easy to do.  But once it's done,
+all folding happens automatically.
+   Here we'll assume you are using an existing syntax file.  Then there is
+nothing more to explain.  You can open and close folds as explained above.
+The folds will be created and deleted automatically when you edit the file.
+
+More about folding by syntax in the reference manual: |fold-syntax|
+
+==============================================================================
+*28.8*	Folding by expression
+
+This is similar to folding by indent, but instead of using the indent of a
+line a user function is called to compute the fold level of a line.  You can
+use this for text where something in the text indicates which lines belong
+together.  An example is an e-mail message where the quoted text is indicated
+by a ">" before the line.  To fold these quotes use this: >
+
+	:set foldmethod=expr
+	:set foldexpr=strlen(substitute(substitute(getline(v:lnum),'\\s','',\"g\"),'[^>].*','',''))
+
+You can try it out on this text:
+
+> quoted text he wrote
+> quoted text he wrote
+> > double quoted text I wrote
+> > double quoted text I wrote
+
+Explanation for the 'foldexpr' used in the example (inside out):
+   getline(v:lnum)			gets the current line
+   substitute(...,'\\s','','g')		removes all white space from the line
+   substitute(...,'[^>].*','','')	removes everything after leading '>'s
+   strlen(...)				counts the length of the string, which
+					is the number of '>'s found
+
+Note that a backslash must be inserted before every space, double quote and
+backslash for the ":set" command.  If this confuses you, do >
+
+	:set foldexpr
+
+to check the actual resulting value.  To correct a complicated expression, use
+the command-line completion: >
+
+	:set foldexpr=<Tab>
+
+Where <Tab> is a real Tab.  Vim will fill in the previous value, which you can
+then edit.
+
+When the expression gets more complicated you should put it in a function and
+set 'foldexpr' to call that function.
+
+More about folding by expression in the reference manual: |fold-expr|
+
+==============================================================================
+*28.9*	Folding unchanged lines
+
+This is useful when you set the 'diff' option in the same window.  The
+|vimdiff| command does this for you.  Example: >
+
+	:setlocal diff foldmethod=diff scrollbind nowrap foldlevel=1
+
+Do this in every window that shows a different version of the same file.  You
+will clearly see the differences between the files, while the text that didn't
+change is folded.
+
+For more details see |fold-diff|.
+
+==============================================================================
+*28.10* Which fold method to use?
+
+All these possibilities make you wonder which method you should choose.
+Unfortunately, there is no golden rule.  Here are some hints.
+
+If there is a syntax file with folding for the language you are editing, that
+is probably the best choice.  If there isn't one, you might try to write it.
+This requires a good knowledge of search patterns.  It's not easy, but when
+it's working you will not have to define folds manually.
+
+Typing commands to manually fold regions can be used for unstructured text.
+Then use the |:mkview| command to save and restore your folds.
+
+The marker method requires you to change the file.  If you are sharing the
+files with other people or you have to meet company standards, you might not
+be allowed to add them.
+   The main advantage of markers is that you can put them exactly where you
+want them.  That avoids that a few lines are missed when you cut and paste
+folds.  And you can add a comment about what is contained in the fold.
+
+Folding by indent is something that works in many files, but not always very
+well.  Use it when you can't use one of the other methods.  However, it is
+very useful for outlining.  Then you specifically use one 'shiftwidth' for
+each nesting level.
+
+Folding with expressions can make folds in almost any structured text.  It is
+quite simple to specify, especially if the start and end of a fold can easily
+be recognized.
+   If you use the "expr" method to define folds, but they are not exactly how
+you want them, you could switch to the "manual" method.  This will not remove
+the defined folds.  Then you can delete or add folds manually.
+
+==============================================================================
+
+Next chapter: |usr_29.txt|  Moving through programs
+
+Copyright: see |manual-copyright|  vim:tw=78:ts=8:noet:ft=help:norl: