Hello,
I'm currently working on upgrading XWiki to use HtmlCleaner 2.29 and it seems https://sourceforge.net/p/htmlcleaner/bugs/228/ has been fixed without taking into account Michael Hamann's comment here: https://sourceforge.net/p/htmlcleaner/bugs/228/#442b
So right now it seems that the following tags are not properly handled as phrasing content:
* data
* embed
* iframe
* img
* math
* object
* picture
* q
* template
* video
Note that we're taking that list of phrasing tag from the spec here https://html.spec.whatwg.org/#phrasing-content-2
You can check the unit test we're using to spot issues there: https://github.com/xwiki/xwiki-commons/blob/xwiki-commons-15.10.6/xwiki-commons-core/xwiki-commons-xml/src/test/java/org/xwiki/xml/internal/html/HTML5HTMLCleanerTest.java#L148-L184