Saxon

It seems like the compile-time type checking for the lookup operator is too strong. For instance the expression //p?innerHTML fails to compile, with the error message:

XPTY0004  The left-hand operand of '?' must be a map or an array; the supplied expression is of type element(Q{}p)

But as I understand it, if the left-hand side resolves to the empty sequence at run-time, then this is not an error. The expression ()?prop returns the empty sequence; it is not an error. (See QT3 tests Lookup-147, Lookup-148, Lookup-149.)