XHP is Facebooks extension to utilize XML fragments and structures directly within PHP source code. Which allows simpler document construction, processing, and sane variable interpolation without having to use DOM functions. It also permits to declare custom :xml:object classes for even quicker templating. Previous versions are available for Zend/PHP5.
minor feature: Permits either type-assert v3 or v4.Requires HHVM 4.32 or above; older versions of HHVM are themselves unsupported.