Yes, this is true even on the hybrid proposal I suggest above, because iframe
, like del
, can be both “flow content” (block level) or “phrase content” (span level). On the other hand, the fact that iframe
can be flowphrase content means that there are legitimate uses for an iframe inside a paragraph, and possibly even at the beginning of a paragraph. So, I think, we shouldn’t make it impossible for authors to write these things. The current proposal allows you to use an iframe
either inside a paragraph (even at the beginning) or as an independent block. The author can choose, it’s just a matter of whether you put the opening tag on a line by itself.
In general, I’m against creating “blind spots” – things that are impossible to express in CommonMark.
Yes, and it has been solved in a variety of ad hoc ways (or in some cases not solved). The hope was that we could do better, and have a principled solution.
As @vitaly notes, HTML5 already allows custom tags, and there have been requests from users to deal with them better.
In addition, we might consider the possibility that someone would target, say, DocBook or another XML format. (Creating a DocBook renderer for cmark or commonmark.js would be quite easy.) In that case they might like the ability to use raw DocBook on occasion. The present proposal supports this kind of thing.