KMail filters. Is it possible to match the = symbol?

If I try to create a filter to match a string that contains the “=” symbol
in it, the filter does not seem to see it.

For example searching for strings like “==/” or “a.asp?did=1” (without the

This fails to match in either free text or as a regular expression match, so
I wonder if there is some special way to doing this.

Thanks for any suggestions.