pub fn write<ET: EngineTypes>(
engine: &mut EngineReferences<'_, ET>,
tk: ET::Token,
) -> TeXResult<Option<Box<WhatsitFunction<ET>>>, ET>pub fn write<ET: EngineTypes>(
engine: &mut EngineReferences<'_, ET>,
tk: ET::Token,
) -> TeXResult<Option<Box<WhatsitFunction<ET>>>, ET>