code: function replace(pattern, replacement, val){
    utils.assertString(pattern, 'pattern');
    utils.assertString(replacement, 'replacement');
    utils.assertString(val, 'val');
    pattern = new RegExp(pattern.string, 'g');
    var res = val.string.replace(pattern, replacement.string);
    return val instanceof nodes.Ident
      ? new nodes.Ident(res)
      : new nodes.String(res);
  }
docs: Returns string with all matches of `pattern` replaced by `replacement` in given `val`
  
  @param {String} pattern
  @param {String} replacement
  @param {String|Ident} val
  @return {String|Ident}
  @api public