character and nothing else. The special characters are @samp{$},
@samp{^}, @samp{.}, @samp{*}, @samp{+}, @samp{?}, @samp{[}, @samp{]} and
@samp{\}. Any other character appearing in a regular expression is
-ordinary, unless a @samp{\} precedes it.
+ordinary, unless a @samp{\} precedes it. (When you use regular
+expressions in a Lisp program, each @samp{\} must be doubled, see the
+example near the end of this section.)
For example, @samp{f} is not a special character, so it is ordinary, and
therefore @samp{f} is a regular expression that matches the string