they return a void string (null in JS) when they can't find matches, rather than throwing an illegal argument exception or returning an empty string, respectively. This fixes a problem when bookmarking about: URIs. bug=331801 r=brettw@gmail.com sr=ben@mozilla.org git-svn-id: svn://10.0.0.236/trunk@193286 18797224-902f-48f8-a5cc-f745e15eee43