Intent to prototype: Implement the MathMLElement interface and the corresponding content attributes

Hi everyone, *Summary*: I'm planning to implement the MathMLElement interface. This means adding support for new MathML content and IDL attributes (namely, from the GlobalEventHandlers, DocumentAndElementEventHandlers, HTMLOrForeignElement, ElementCSSInlineStyle mixins) that already exist for HTML

Intent to unship: MathML menclose notation "radical"

Hi, In [1] I intend to unship the value "radical" for the notation attribute of the menclose element. It will first be disabled in Nightly and deprecation warnings/counters will be used in other channels. The MathML CG agreed to remove this value from the MathML Core spec [2]. For the record, thi