An active selection is a property of the file, not of a Layer.
»activeDocument« is no property of Layer, either, so
artset.activeDocument.selection.selectAll
makes no sense.
And even if you remove »artset.« you still miss the brackets.
If you bothered to consult ESTK’s Object Model Viewer you could verify which Properties and Methods exist for an Object (see screenshot for an example for »Layer«).
