expressions can have subexpressions---after a simple string search, the
only information available is about the entire match.
+ Every successful search sets the match data. Therefore, you should
+query the match data immediately after searching, before calling any
+other function that might perform another search. Alternatively, you
+may save and restore the match data (@pxref{Saving Match Data}) around
+the call to functions that could perform another search.
+
A search which fails may or may not alter the match data. In the
past, a failing search did not do this, but we may change it in the
future. So don't try to rely on the value of the match data after