code: function a(string $type = ''): self {
      return mb_strlen($type) ? $this->expect($this->target, isType($type)) : $this;
    }
docs: Reports an error if the target is not of the specified type.
  This method can also be used as language chain.
  @param string $type The type to check. Specify an empty string to use as language chain.
  @return self This instance.