Return the documentation string of FUNCTION.
Unless a non-nil second argument RAW is given, the
string is passed through `substitute-command-keys'.

Return the documentation string that is SYMBOL's PROP property.
Third argument RAW omitted or nil means pass the result through
`substitute-command-keys' if it is a string.

This differs from `get' in that it can refer to strings stored in the
`etc/DOC' file; and that it evaluates documentation properties that
aren't strings.

Used during Emacs initialization to scan the `etc/DOC...' file.
This searches the `etc/DOC...' file for doc strings and
records them in function and variable definitions.
The function takes one argument, FILENAME, a string;
it specifies the file name (without a directory) of the DOC file.
That file is found in `../etc' now; later, when the dumped Emacs is run,
the same file name is found in the `doc-directory'.

Substitute key descriptions for command names in STRING.
Each substring of the form \[COMMAND] is replaced by either a
keystroke sequence that invokes COMMAND, or "M-x COMMAND" if COMMAND
is not on any keys.

Each substring of the form \{MAPVAR} is replaced by a summary of
the value of MAPVAR as a keymap.  This summary is similar to the one
produced by `describe-bindings'.  The summary ends in two newlines
(used by the helper function `help-make-xrefs' to find the end of the
summary).

Each substring of the form \<MAPVAR> specifies the use of MAPVAR
as the keymap for future \[COMMAND] substrings.
\= quotes the following character and is discarded;
thus, \=\= puts \= into the output, and \=\[ puts \[ into the output.

Return the original STRING if no substitutions are made.
Otherwise, return a new string, without any text properties.