callFunction(e, t, r, a, i) {
    var l = {
      funcName: e,
      parser: this,
      token: a,
      breakOnTokenText: i
    }, s = an[e];
    if (s && s.handler)
      return s.handler(l, t, r);
    throw new G("No function handler for " + e);
  }
Parses a group, essentially returning the string formed by the
brace-enclosed tokens plus some position information.