31.6.1 Info Documentation Lookup
For C, Lisp, and other languages that have documentation in Info,
you can use C-h S (
info-lookup-symbol) to view the Info
documentation for a symbol used in the program. You specify the
symbol with the minibuffer; the default is the symbol appearing in the
buffer at point. For example, in C mode this looks for the symbol in
the C Library Manual.
The major mode determines where to look for documentation for the
symbol—which Info files to look in, and which indices to search.
You can also use M-x info-lookup-file to look for documentation
for a file name.
This feature currently supports the modes AWK, Autoconf, Bison, C,
Emacs Lisp, LaTeX, M4, Makefile, Octave, Perl, Scheme, and Texinfo,
provided you have installed the relevant Info files, which are
typically available with the appropriate GNU package.