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Description
It has come to my attention that customized built-in elements are not supported on some browsers (e.g. Safari). Hence it would be better to introduce custom elements. With the <menu is="context-menu"> it will not be a problem, but in case of <details is="context-menu-group"> I have to decide on the way the element’s markup should look like in the end. It might be best to make the syntax look as similar to the built-in elements as possible.