The ruby api [1] has some useful information on the scan function. The page you are interested in is probably [2]. If you are going to be manipulating html documents, you might want to check out Hpricot [3], or some other html parser.
[1] http://www.ruby-doc.org/core/ [2] http://www.ruby-doc.org/core/classes/StringScanner.html [3] http://code.whytheluckystiff.net/hpricot/
