code: function(subjectString, searchString, position) {
                  position = position || 0;
                  return subjectString.substr(position, searchString.length) === searchString;
              }
docs: Determines whether subjectString begins with the characters of searchString.
  @param {String} subjectString The string to analyse.
  @param {String} searchString The characters to be searched for at the start of subjectString.
  @param {Number} position The position in subjectString at which to begin searching for searchString; defaults to 0.
  @return {Boolean} true if the given characters are found at the beginning of the string; otherwise, false.