The WFS E/R assumes property selection, as defined in the Testbed 14 WFS3 "extension" (actually, just a paragraph in the Testbed 14 WFS E/R), is there.
It's easy to add (we just need to translate properties to propertyNames in the URL), extra points for doing it right and adding its presence in the API document (and possibly a new endpoint describing the list of properties, that we could implement by re-routing DescribeFeatureType).
The WFS E/R assumes property selection, as defined in the Testbed 14 WFS3 "extension" (actually, just a paragraph in the Testbed 14 WFS E/R), is there. It's easy to add (we just need to translate properties to propertyNames in the URL), extra points for doing it right and adding its presence in the API document (and possibly a new endpoint describing the list of properties, that we could implement by re-routing DescribeFeatureType).