code: function isString(o)  {
      return o !== undefined && o !== null &&
            (typeof o === "string" || o.constructor === String);
  }
docs: Faster match operation analogues: Math.floor(f)  =>  ~~(a) Math.round(f)  =>  (f + 0.5) | 0 
  Check if the given value is string
  @param {Object} v a value.
  @return {Boolean} true if the given value is string
  @method isString
  @for zebkit