The description of "group-by" states "The name of each grouping variable must be equal (by the eq operator on expanded QNames) to the name of a bound variable in the input tuple stream; otherwise a static error is raised [err:XQST0094]."

But the definition of XQST0094 states "In the group by clause of a FLWOR expression, it is a static error if the name of a grouping variable is not equal (by the eq operator on expanded QNames) to the name of a variable that is bound by a for or let clause that precedes the group by clause."

This leaves it unclear whether it is permissible for the grouping variable to be one that is bound by a previous count, group-by, or window clause.

(I'm also puzzled by the qualifier "bound" in "bound variable". Is it possible to have unbound variables in the tuple stream?)