> If you have pattern matching needs that go beyond this, consider writing a user-defined function in Perl or Tcl.
I think Perl and Tcl are no more the most common languages to write user-defined functions.
What would be the most common? pl/python only comes in untrusted form, so can only be used by the superuser. I think that rules it out as a general recommendation. And SQL and PL/pgSQL don't solve the problem. Are there any outside-of-standard-distribution languages which could qualify as common?
Maybe just remove "in Perl or Tcl" and provide a link to the general docs of user-defined functions.