get_group (REXML::XPathParser)

    # File rexml/xpath_parser.rb, line 586
      def get_group string
    			ind = 0
    			depth = 0
    			st = string[0,1]
    			en = (st == "(" ? ")" : "]")
    			begin
    				case string[ind,1]
    				when st
    					depth += 1
    				when en
    					depth -= 1
    				end
    				ind += 1
    			end while depth > 0 and ind < string.length
    			return nil unless depth==0
    			[string[ind..-1], string[0..ind-1]]
    		end