URLM_ADD_OVERRIDE <browser> <pattern>

Add an override, for use with /urlm_open (q.v.)

<browser> is the "tag", previously defined with URLM_ADD_BROWSER.

<pattern> is a Perl regular expression (regex). Any URL matching the
regex (case-insensitive) will be open with <browser>.

It's probably best to avoid conflicting/overlapping patterns, although
it can be done if you remember that the regexes are checked against each
URL in the order they are displayed in /urlm_list_overrides (which is
in fact the order in which they were defined).