rendering operations on a specific feature are performed
This allows symbol layer subclasses to know when a set of rendering
operations all relate to a single feature, e.g. when a number
of polygons are rendered which all belong to the same multi-polygon
geometry attached to a single feature.
Without these hooks, symbol layer subclasses have no stable method
of knowing that these parts all relate to a single feature, or
have no means of knowing when the final part of that feature has
been rendered.
491a4a794d