@item
In C code, any C function or typedef is a tag, and so are definitions of
@code{struct}, @code{union} and @code{enum}.
-@code{#define} macro definitions and @code{enum} constants are also
+@code{#define} macro definitions, @code{#undef} and @code{enum}
+constants are also
tags, unless you specify @samp{--no-defines} when making the tags table.
Similarly, global variables are tags, unless you specify
@samp{--no-globals}. Use of @samp{--no-globals} and @samp{--no-defines}