columns, counting from 0 at the left margin. The column position is the
sum of the widths of all the displayed representations of the characters
between the start of the current line and point.
-
-For an example of using @code{current-column}, see the description of
-@code{count-lines} in @ref{Text Lines}.
@end defun
@deffn Command move-to-column column &optional force
text at point (@pxref{Completion in Buffers}).
@end defopt
+@cindex literate programming
+@cindex multi-mode indentation
+ Some major modes need to support embedded regions of text whose
+syntax belongs to a different major mode. Examples include
+@dfn{literate programming} source files that combine documentation and
+snippets of source code, Yacc/Bison programs that include snippets of
+plain C code, etc. To correctly indent the embedded chunks, the major
+mode needs to delegate the indentation to another mode's indentation
+engine (e.g., call @code{c-indent-defun} for C code or
+@code{python-indent-line} for Python), while providing it with some
+context to guide the indentation. The following facilities support
+such multi-mode indentation.
+
+@defvar prog-indentation-context
+This variable, when non-@code{nil}, holds the indentation context for
+the sub-mode's indentation engine provided by the superior major mode.
+The value should be a list of the form @code{(@var{first-column}
+@w{(@var{start} . @var{end})} @code{prev-chunk})}. The members of the
+list have the following meaning:
+
+@table @var
+@item first-column
+The column to be used for top-level constructs. This replaces the
+default value of the top-level column used by the sub-mode, usually
+zero.
+@item start
+@itemx end
+The region of the code chunk to be indented by the sub-mode. The
+value of @var{end} can be @code{nil}, which stands for the value of
+@code{point-max}.
+@item prev-chunk
+If this is non-@code{nil}, it should provide the sub-mode's
+indentation engine with a virtual context of the code chunk. Valid
+values include:
+
+@itemize @minus
+@item
+A string whose contents is the text the sub-mode's indentation engine
+should consider to precede the code chunk. The sub-mode's indentation
+engine can add text properties to that string, to be reused in
+repeated calls with the same string, thus using it as a cache. An
+example where this is useful is code chunks that need to be indented
+as function bodies, but lack the function's preamble---the string
+could then include that missing preamble.
+@item
+A function. It is expected to be called with the start position of
+the current chunk, and should return a cons cell
+@w{@code{(@var{prev-start} . @var{prev-end})}} that specifies the
+region of the previous code chunk, or @code{nil} if there is no previous
+chunk. This is useful in literate-programming sources, where code is
+split into chunks, and correct indentation needs to access previous
+chunks.
+@end itemize
+@end table
+@end defvar
+
+The following convenience functions should be used by major mode's
+indentation engine in support of invocations as sub-modes of another
+major mode.
+
+@defun prog-first-column
+Call this function instead of using a literal value (usually, zero) of
+the column number for indenting top-level program constructs. The
+function's value is the column number to use for top-level constructs.
+When no superior mode is in effect, this function returns zero.
+@end defun
+
+@defun prog-widen
+Call this function instead of @code{widen} to remove any restrictions
+imposed by the mode's indentation engine and restore the restrictions
+recorded in @code{prog-indentation-context}. This prevents the
+indentation engine of a sub-mode from inadvertently operating on text
+outside of the chunk it was supposed to indent, and preserves the
+restriction imposed by the superior mode. When no superior mode is in
+effect, this function just calls @code{widen}.
+@end defun
+
@node Region Indent
@subsection Indenting an Entire Region
@item help-echo
@kindex help-echo @r{(text property)}
-@cindex tooltip
+@cindex tooltip for help strings
@anchor{Text help-echo}
If text has a string as its @code{help-echo} property, then when you
move the mouse onto that text, Emacs displays that string in the echo
-area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
-Manual}).
+area, or in the tooltip window (@pxref{Tooltips}).
If the value of the @code{help-echo} property is a function, that
function is called with three arguments, @var{window}, @var{object} and
coding instead.
@end defun
+@defun buffer-hash &optional buffer-or-name
+Return a hash of @var{buffer-or-name}. If @code{nil}, this defaults
+to the current buffer. As opposed to @code{secure-hash}, this
+function computes the hash based on the internal representation of the
+buffer, disregarding any coding systems. It's therefore only useful
+when comparing two buffers running in the same Emacs, and is not
+guaranteed to return the same hash between different Emacs versions.
+It should be somewhat more efficient on larger buffers than
+@code{secure-hash} is, and should not allocate more memory.
+@c Note that we do not document what hashing function we're using, or
+@c even whether it's a cryptographic hash, since that may change
+@c according to what we find useful.
+@end defun
+
@node Parsing HTML/XML
@section Parsing HTML and XML
@cindex parsing html