The next alternative is for @samp{a*} to match only two @samp{a}s.
With this choice, the rest of the regexp matches successfully.@refill
+Nested repetition operators can be extremely slow if they specify
+backtracking loops. For example, @samp{\(x+y*\)*a} could take hours to
+match the sequence @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}. The
+slowness is because Emacs must try each imaginable way of grouping the
+35 @samp{x}'s before concluding that none of them can work. To make
+sure your regular expressions run fast, check nested repetitions
+carefully.
+
@item +
@cindex @samp{+} in regexp
is a suffix operator similar to @samp{*} except that the preceding