How can I stroke a selection?
The way to do it is to use the Outline feature
Make a selection
Go, Select > Outline
You can decide where the Outline is applied. Outside the selection boundary, both sides (centre) or inside.
Drag the slider or set an amount in pixels.
This is outside the selection.
It can then be filled with anything. Edit > Fill
It can be partially stroked by using a paint brush.
Or you can even ad