Use of "Metadata content" in <layer>'s content model #84
Description
Content model:
If the src attribute is present: Empty. If no src attribute is present: Metadata content describing nested Map Markup Language content
"Metadata content" is a specific list of HTML elements, plus "Elements from other namespaces whose semantics are primarily metadata-related (e.g. RDF) are also metadata content."
https://html.spec.whatwg.org/multipage/dom.html#metadata-content-2
If you want to allow only MapML elements here, don't use "metadata content".