code: function stripNegate(val, negate) {
      negate = escape(negate || constants_1.NEGATE_CHAR);
      var exp = new RegExp('^' + negate);
      return val.replace(exp, '');
  }
docs: Strips negate chars from flag.
  
  @param val the value to be stripped.
  @param negate the characters denoting negate.