XMF has a version of Request that is regularly synchronized with newer versions, and will be the definitive version starting with XOOPS 2.5.8. This is how the same code can look with XMF:
$input= Xmf\Request::getString('input','');
You can combine this with the tips under namespaces, and expand to a few more input fields for a look at a more typical use case:
use Xmf\Request;// ...$input=Request::getString('input','');$id=Request::getInt('id','');$op=Request::getCmd('op','display');
Autoloading for the Xmf namespace is managed by a PSR-4 autoloader. The same autoloader also manages autoload for several libraries that XMF depends on. This autoloader will be standard in future XOOPS versions.