Which characters are valid in tab_merge_overlay column 4?

• Article Type: General
• Product: Aleph
• Product Version: 20

Description:
We are trying to merge some incoming bib records. Many of these records have a new URL and we want to discard the existing URL in favor of the new one. But only the existing URLs that are part of the MARCit record set we are importing, not URLs from another site.
We're trying to reject existing 856## or 956## from owens.mit.edu, but keep any others.

43 2 N 956##,u,*owens.edu*

does not work. It doesn't seem to like the period character.

43 2 N 956##,u,*owens*

does work. However, we're afraid other URLs could possibly contain just that one word, and would like to use something longer or more distinctive.

We've also tried matching with other portions of the URL, containing characters such as %. Some strings are working, others are not.

Is there any list of characters that are valid for this kind of subfield content matching? Or is there a single character wildcard? Neither # nor ? seems to do it.
I've been unsuccessful searching the documentation.

Resolution:
We found that the dot period is not a valid character for tab_merge_overlay string filtering.