Use this function to register a filter factory with the name given by
filterpattern. filterpattern
can be either a normal string name (i.e. myfilter) or
a global pattern (i.e. myfilterclass.*) to allow a single
filter to perform different operations depending on the exact name of the filter
invoked (i.e. myfilterclass.foo, myfilterclass.bar,
etc...)
Note: Filters registered by a loadable extension must be certain to call php_stream_filter_unregister_factory() during MSHUTDOWN.