Hello,
I'm working on a script font (open type for mac) that has very long ascenders and descenders.
When I test it in Indesign with an automatic line space, the problem is the these ascenders and descenders cross themselves from a line to another.
It has a standard UPM value of 1000; I tried various values in the advanced vertical metrics with no effect on the line space.
I wonder how I can change this ?
Cheers,
Serge

Dear Serge, did you ever find an answer to this question?

InDesign does line spacing based on point size and leading. The default is em + 20%.

If you have your ascenders and descenders crossing over, they are probably just too darn long, and you need to rescale the font or redefine the em size.

An "average font" has a cap height of about 0.7 em and x-height of about 0.5 em, with ascender of maybe 0.75 em and descender of maybe 0.25 em. The 20% extra added by InDesign is then all white space.

So if you deviate from the typical by more than 20%, well, yes, you'll get clashes. Either expect users to change the leading in serious publishing apps, or make the font smaller on the body.