Per discussion on the open ui discord initiated by @tbondwilkinson, there is some value in further identifying the differences between a "popup" and a "modal dialog" and why the disallowed elements section calls them out as not supporting popup.

Potentially adding to the goals section (or non-goals), examples, or even expanding the initial background section to help further clarify the differences between UI elements that "float" on screen and how not all floating content should be considered a "popup".

@tbondwilkinson please do add any of your thoughts here, as I'm sure my brief intro to the topic is not doing justice to your concerns.