Add class=“layer” to each layer element. This happens when calling
createLayer() or any call to identifyLayers(). This happens with new
drawings and when opening legacy drawings, so it’s fully backwards
compatible.
svg-editor.js elementChanged() looks for g.layer as an addition test
for calling populateLayers() which updates the layers panel.
Addition tests for class=“layer” added to draw_test.html.
Fixed Firefox exception in draw_test.html.