textBox becomes an inline node carrying block content, like the frame both
formats write, so "in line with text" really is in the line and a box reaches
a table cell or a list item through their paragraphs. Both exports write it
where it sits (an as-char draw:frame / a wp:inline drawing) and both imports
leave it there, which drops the hoisting machinery on either side.
Two guards the schema cannot express: no box inside a box, and a selection
reaching into a box grows to the box's bounds rather than dissolving it.