Pattern Matching a sting value

How in XSLT 1.0 do you interogate a specific portion of a string?

$stg = "font:...;font-family:Arial;color:#FFFFF;...."

I am only interested in the portion of this string that contains Arial.

Thanks in advance for any insight

- Scott

XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list