Function xsltRegisterExtModuleFunction 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn xsltRegisterExtModuleFunction(
    name: *const xmlChar,
    URI: *const xmlChar,
    function: Option<xmlXPathFunction>,
) -> c_int

xsltRegisterExtModuleFunction (extensions.c): register an XPath extension function (name in a module URI).

UPSTREAM-PARITY

int xsltRegisterExtModuleFunction(const xmlChar *name, const xmlChar *URI,
                                  xmlXPathFunction function);