I noticed that some expressions could belong to multiple categories:
One such example is collect(expression, group_by, filter)
Returns the multipart geometry of aggregated geometries from an expression.
For now, it resides in the "Aggregates" category, but just as well it
could reside in the "Geometry" category. Most likely, there are other
expression functions that might reside in multiple categories.
Question: should we in the future allow that an expression belongs to
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