> I notice in the BaseX GUI that when I execute an XQuery script that includes type checks (e.g., let $x as element(stuff) := <stuff/>) the compilation report tells me that BaseX removes the type checks. How should I understand this removal? I can see that BaseX is performing type-checking because if I specify the wrong type, an error is thrown. I'd be grateful for any insights anyone can provide about what the "remove type check" messages mean?

This info reflects what the optimizer does before evaluating your query. In the given case, the explicit type check is removed from the internal query execution plan. The reason is that it can be determined at compile time that the bound expression will always have the requested type. If the input type may differ from the requested one, the check will be preserved.