This proposal extends the DocumentOrShadowRoot mixin with a new method getCascadeLayers(), which returns the names of all the CSS cascade layers defined in the tree scope, sorted by the layer ordering.
DocumentOrShadowRoot.getCascadeLayers() allows browser DevTools to present a visualization of all layers, for example:
Without this extension, DevTools have to manually collect the @layer rules from the stylesheets and reconstruct the full layer names and the sorted layer ordering.