diff options
| -rw-r--r-- | doc/lispref/searching.texi | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi index 83c154938cd..c8a12bdd66b 100644 --- a/doc/lispref/searching.texi +++ b/doc/lispref/searching.texi @@ -338,16 +338,14 @@ first tries to match all three @samp{a}s; but the rest of the pattern is The next alternative is for @samp{a*} to match only two @samp{a}s. With this choice, the rest of the regexp matches successfully. -@strong{Warning:} Nested repetition operators can run for an -indefinitely long time, if they lead to ambiguous matching. For +@strong{Warning:} Nested repetition operators can run for a very +long time, if they lead to ambiguous matching. For example, trying to match the regular expression @samp{\(x+y*\)*a} against the string @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could take hours before it ultimately fails. Emacs must try each way of grouping the @samp{x}s before concluding that none of them can work. -Even worse, @samp{\(x*\)*} can match the null string in infinitely -many ways, so it causes an infinite loop. To avoid these problems, -check nested repetitions carefully, to make sure that they do not -cause combinatorial explosions in backtracking. +In general, avoid expressions that can match the same string in +multiple ways. @item @samp{+} @cindex @samp{+} in regexp |