Function matchGroup( str, regex )

Description:
Returns the first grouped expression matched in a string defined by a regular expression. A grouped expression is one enclosed in parentheses.
Parameters:
str (String)
string to match against
regex (String)
regular expression containing a grouped section
Return Value (String):
contents of the matched group (or null, if regex didn't match str)
Example:
matchGroup("NGC28948b","NGC([0-9]*)") = "28948"
Signature:
String matchGroup(String, String)