Function libxslt::bindings::xmlXPathRegisterVariableLookup

pub unsafe extern "C" fn xmlXPathRegisterVariableLookup(
    ctxt: *mut _xmlXPathContext, 
    f: Option<unsafe extern "C" fn(*mut c_void, *const u8, *const u8) -> *mut _xmlXPathObject>, 
    data: *mut c_void
)