f(...)}, by writing {\tt f(...)@E@p}, for expression metavariable {\tt E}
and position metavariable {\tt p}.
+Other kinds of metavariables can also be attached using \texttt{@} to any
+token. In this case, the metavariable floats up to the enclosing
+appropriate expression. For example, {\tt 3 +@E 4}, where {\tt E} is an
+expression metavariable binds {\tt E} to {\tt 3 + 4}. A particular case is
+{\tt Ps@Es}, where {\tt Ps} is a parameter list and {\tt Es} is an
+expression list. This pattern matches a parameter list, and then matches
+{\tt Es} to the list of expressions, ie a possible argument list,
+represented by the names of the parameters.
+
\begin{grammar}
\RULE{\rt{ids}}
\CASE{\NT{COMMA\_LIST}\mth{(}\NT{pmid}\mth{)}}