suboptimal visualization of "unusual" whitespace and non-printing characters

the following text (represented as xml herein; can be pasted into a linguist .ts file, for example)

1. nbsp( )
2. ensp( ) emsp( ) thinsp( )
3. shy(­) zwnj(‌) zwj(‍)
4. lrm(‎) rlm(‏)

is not visualized properly:
1. the non-breaking space is visualized like a normal space.
2. the "special-width" spaces are not visualized at all.
3. these non-printable characters have no visual representation at all. maybe this needs to be a separate task, as visualizing these actually changes the text layout.
4. these are like 3., except that they are sort-of visualized by the cursor, so one might argue whether additional visualization is necessary. i don't have the RTL/LTR expertize to answer that.