isAnchorable feature

Problem

Currently all StaticSubVertex can be anchor of an edge. But what if I want to have "dead" StaticSubVertex where I don't want edges to attache?

Workaround

Currently, we adjust to query to something that is no anchor, e.g. with a @PARENT

Idea

feature isAnchorable for SubVertexA or even ShapedObject. By default true for backwards compatibility. If set to false, it is ignored when looking for anchors.

Benefit

Explicit "decoration only" elements without accidentically edges connecting to.