note sutch This:<br> <code>(.*?)\s*(.*?)\s*</code><br> can be problematic. Since LABEL and PARAMETER must not contain spaces, try replacing that portion with something like:<br> <code>([^\s]+)\s+([^\s]+)?</code><p> I'd also suggest that you change *? to simply *, since * denotes 0 or more occurances.<p> Probably the biggest problem is the:<br> <code>(.+?)</code><br> which occurs just before:<br> <code><%end_\1%></code><br> and matches to the end of the string, which then causes the regex engine to backtrack each time it cannot find each "end" tag.<p> You may also want to take a look at the book "Mastering Regular Expressions" by Jeffrey E. Friedl. See [id://21667|Mastering Regular Expressions] for a review. 240648 240648