In Pub 519 https://www.irs.gov/pub/irs-pdf/p519.pdf under section Interrupted Period of Residence, there is a special rule to "tax on your U.S. source gross income and gains on a net basis at the graduated rates applicable to individuals". When I try to see what this means and how to calculate this, it says "For information on how to figure the special tax, see Expatriation Tax, later." which is not helpful because Expatriation Tax does not seem relate to this at all.
I am guessing it's about some US income such as capital gain that will be taxed as ordinary income under nonresident alien tax bracket (as single filer or married filing separately since non resident is not allowed for joint filing), but I am not sure. I know this may be a very specific situation, but has someone come across this before?
