Tabs default to every 1”, and can be set in points using the tabrack property:

nlTabrack 96 ¯200 220
nlSet 'tabrack' 144  ¯600

Negative tabs are right-aligned, centred and decimal tabs are not supported. To skip to the next tab, embed ŒTCHT or the string <tab> in the input to nlFlow. Note that nlPlace does not process HTML tags, so does not notice tabs. All tabs are relative to the left edge of the current frame and disregard indents.

If you set tabstops beyond the right edge of the frame, no check is made on the positioning, and your text will appear outside the frame.