GitLab

	(Commands for Insertion): Removed split-line since it's not
	relevant for Lisp programming.
	(Yank Commands): Rewrite introduction.
	(Undo): Clarify.
	(Maintaining Undo): Clarify.  Document undo-ask-before-discard.
	(Filling): Remove redundant comment.  Clarify return value of
	current-justification.
	(Margins): Minor clarifications.
	(Adaptive Fill): Update default value of adaptive-fill-regexp.
	(Sorting): Update definition of sort-lines.
	(Columns): Clarify behavior of sort-columns.
	(Indent Tabs): Link to Tab Stops in Emacs manual.
	(Special Properties): Clarify.
	(Clickable Text): Mention Buttons package.