@cindex @file{DOC} (documentation) file
Sometimes, Emacs does not keep documentation strings in memory.
There are two such circumstances. Firstly, to save memory, the
-documentation for preloaded functions and variables (including
-primitives) is kept in a file named @file{DOC}, in the directory
-specified by @code{doc-directory} (@pxref{Accessing Documentation}).
-Secondly, when a function or variable is loaded from a byte-compiled
-file, Emacs avoids loading its documentation string (@pxref{Docs and
-Compilation}). In both cases, Emacs looks up the documentation string
-from the file only when needed, such as when the user calls @kbd{C-h
-f} (@code{describe-function}) for a function.
+documentation for primitive functions (@pxref{What Is a Function}) and
+built-in variables is kept in a file named @file{DOC}, in the
+directory specified by @code{doc-directory} (@pxref{Accessing
+Documentation}). Secondly, when a function or variable is loaded from
+a byte-compiled file, Emacs avoids loading its documentation string
+(@pxref{Docs and Compilation}). In both cases, Emacs looks up the
+documentation string from the file only when needed, such as when the
+user calls @kbd{C-h f} (@code{describe-function}) for a function.
Documentation strings can contain special @dfn{key substitution
sequences}, referring to key bindings which are looked up only when