I'm inserting elements in a docx document via docx4j and I want my new elements to be on front (always visible over other elements that could overlap).
I think that in order to accomplish my target I have to set to the maximum value the relativeHeight attribute of the wp:anchor tag.
So my question is: which is the maximum value allowed?
Documentation at http://www.officeopenxml.com/drwPicFloating.php doesn't specify it.
Per the spec (see eg anchor_2.html) it is defined by the XML Schema to be unsignedInt datatype, the max value for which is what can fit in a word of 32 bits (which, happily, matches your empirical finding).
I didn't see anything in [MS-OE376] or [MS-OI29500] which adds to this.