I thought that a level would have been an embedded svg tag in the file

But I verified, it's not. A level is a simple g tag

Are there any cases in which Inkscape writes an embedded svg tag ?

Can Inkscape read a file with embedded svg tags ?

I ask because I'm considering the possibility to reproduce a screen of an Android app in svg and I saw an impressive talk about svg (this one https://www.youtube.com/watch?v=SeLOt_BRAqc ) in which he demonstrates some tag nesting (among other fun things)

I'd like to realize an area with

a ruler column on the left that scrolls ONLY vertically
a ruler row, on the upper boundary, that scrolls ONLY horizontally
a central area that scrolls BOTH horizontally and vertically

I was thinking that embedded svg tags (with their own viewport) would have been fit for this but I was hoping to use Inkscape to sketch them

Does any of this make sense ?