Mathematical content not available for phrased contenteditable fields.

[Bram]

When using the inline editor on phrased content​https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Content_categories#Phrasing_content the option to add math with the Mathematical Content plugin is disabled.

According to the specs the <math> element is considered valid phrased content. I guess there is some unnecessary content filtering going on that prevents me from using the plugin? If so, is there a list where I can check which elements/plugins are allowed for each content type (flow or phrased)?