element vertex

diagram
properties	content  complex
used by	elements  leftControls points polygon polyline rightControls track wire
attributes	Name   Type   Use   Default   Fixed   annotation at point required         documentation The location of the vertex.
annotation	documentation A vertex for a curve or polyline/polygon.

attribute vertex/@at

type	point
properties	isRef  0 use  required
facets	pattern  [-]*[0-9.]+,[-]*[0-9.]+
annotation	documentation The location of the vertex.