The only variables provided by the eventcatcher widget are the ones described at https://tiddlywiki.com/#EventCatcherWidget
The current implementation for providing event variables isn’t particularly scaleable because the provision of each variable needs to be hardcoded into the widget. However, now that we have JSON filter operators in the core, the way to proceed would be to provide all event properties as a JSON object to the actions invoked, which can then query and extract properties as needed. Similarly I use a macro that returns other properties that I need, such as an elements width or height or scrollY. We need to find a flexible means to introduce the same affordance to the core.
A PR for this would be very welcome if someone has the skillset and opportunity to work on it.