Completes the process of a temporary sub-parser redirection.
This function exists to collect the user_data allocated by a
matching call to g_markup_parse_context_push(). It must be called
in the end_element handler corresponding to the start_element
handler during which
g_markup_parse_context_push() was called.
You must not call this function from the error callback — the
user_data is provided directly to the callback in that case.
This function is not intended to be directly called by users interested in invoking subparsers. Instead, it is intended to be used by the subparsers themselves to implement a higher-level interface.