public function has( $tag, $callback = false ) {
		$has = ! empty( $this->hooks[$tag] );

		// Return early if we already know it's false.
		if ( false === $callback || false === $has )
			return $has;

		// Cycle through the hook priorities to find the callback we're looking for.
		foreach ( (array) array_keys( $this->hooks[$tag] ) as $priority )
			if ( in_array( $callback, $this->hooks[$tag][$priority] ) )
				return $priority;

		return false;
	}