bell, @samp{\b} for back space, @samp{\e} for escape, @samp{\f} for
formfeed, @samp{\n} for newline, @samp{\r} for carriage return,
@samp{\t} for tab, and @samp{\v} for vertical tab. In addition,
-@samp{\d} stands for the @code{DEL} character. Shy groups are not
-supported by @command{etags}.
+@samp{\d} stands for the @code{DEL} character. Otherwise,
+the regular expression syntax is the same as Emacs
+except that backslash escapes are the same
+as GNU grep (which means, for example, that shy groups are not supported),
+and @samp{[:ascii:]}, @samp{[:multibyte:]}, @samp{[:nonascii:]},
+@samp{[:word:]}, and @samp{[:unibyte:]} are not supported.
Ideally, @var{tagregexp} should not match more characters than are
needed to recognize what you want to tag. If the syntax requires you
needed are unavoidably matched by \fItagregexp\fP, it may be useful to
add a \fInameregexp\fP, to narrow down the tag scope. \fBctags\fP
ignores regexps without a \fInameregexp\fP. The syntax of regexps is
-the same as in emacs, except that shy groups are not supported.
+the same as in Emacs, except that backslash escapes are the same
+as GNU grep (which means, for example, that shy groups are not supported),
+and \fB[:ascii:]\fP, \fB[:multibyte:]\fP, \fB[:nonascii:]\fP,
+\fB[:word:]\fP, and \fB[:unibyte:]\fP are not supported.
The following character escape sequences are supported:
\\a, \\b, \\d, \\e, \\f, \\n, \\r, \\t, \\v, which respectively
stand for the ASCII characters BEL, BS, DEL, ESC, FF, NL, CR, TAB, VT.