src/includes/classes/Core/Error.php
public function message(string $slug = ''): string
    {
        $slug     = $slug ?: $this->slug();
        $messages = $this->messages($slug);
        return $messages[0] ?? $this->default_message;
    }
public function message(string $slug = ''): string
    {
        $slug     = $slug ?: $this->slug();
        $messages = $this->messages($slug);
        return $messages[0] ?? $this->default_message;
    }
Get error slug.

@since 160710 Error utils.

@param string $slug Error slug.

@return string Error message.