Follow-up to bug 52917: With the current implementation, style bleeds may still happen on components within components. In such a case the accessor check for the nested component can be circumvented by a shadow pseudo-element selector for the outer component. For example:
Assume you have a media control panel component that defines a container for button controls. This container is given a pseudo-ID "panel", e.g., to allow styling its background. The container also has one or more children of its own for the individual buttons, which are defined as separate components.
In this case, a selector such as "::panel *" would bleed into the buttons, even if they are set to not allow selectors through. That check would be circumvented by the presence of the "::panel" pseudo-element selector, even though this is meant for the outer component.
*** This bug has been marked as a duplicate of bug 62218 ***