Collect every data-leaf descended from start.
Used by group-layer controls that need to fan out to actual materials.
"Data-leaf" is the whole geometry vocabulary, not a fixed list: a group-level
opacity / gamma / colormap control must reach every leaf underneath it, so a
geometry type omitted here would silently ignore its ancestors' attributes.
Collect every data-leaf descended from
start. Used by group-layer controls that need to fan out to actual materials."Data-leaf" is the whole geometry vocabulary, not a fixed list: a group-level opacity / gamma / colormap control must reach every leaf underneath it, so a geometry type omitted here would silently ignore its ancestors' attributes.