Routing Code - question

In routing.rb, what is the purpose of the following piece of code:

class Regexp #:nodoc:
  def number_of_captures"|#{source}").match('').captures.length

Does this method not always return 0? It's always going to match ''
with the blank spot before the | and therefore will have no captures."|(.)").match("a").captures.length

=> 1

Just responding to see KC's response since Google Groups is borked and
not showing the last response in each thread.