code: function toBoolean(str, fallback) {
      if (typeof str === 'boolean') {
          return str;
      }
      if (REGEXP_TRUE.test(str)) {
          return true;
      }
      if (REGEXP_FALSE.test(str)) {
          return false;
      }
      return fallback;
  }
docs: convert string to strict boolean.
  
  @param {string|boolean} str
  @param {boolean} [fallback]
  @returns {boolean}