class REXML::Parsers::XPathParser

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