docs: function mentionsPredicate(str) {
    // null/empty check
    if (!str) {
      return false;
    // has @ symbol
    } else if (str.indexOf('@') < 0) {
      return false;
    // has @ symbol as first char
    } else if (str[0] !== '@') {
      return false;
    // contains non-word chars
    } else if ((/[^\w\s]/).test(str.slice(1))) {
      return false;
    // if ends with @
    } else if (str[str.length - 1] === '@') {
      return false;
    }
    return true;
  }