lib/Assertion.php
function a(string $type = ''): self {
    return mb_strlen($type) ? $this->expect($this->target, isType($type)) : $this;
  }
function a(string $type = ''): self {
    return mb_strlen($type) ? $this->expect($this->target, isType($type)) : $this;
  }
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.