[Interest] system, general and fixed font on Linux

[René J.V. Bertin]

Hi,

Looking at the output from the qtdiag app from a newly built Qt 5.5.0 install (installed into /opt/local), I noticed that its system, general and fixed width fonts were fonts I apparently chose one way or another, at some point in the past.
Where is this information obtained from, I can't seem to find a candidate settings file under ~/.local or ~/.config ?

My other question would be whether that file is also consulted on OS X and/or MS Windows, but I guess I'll figure that out for myself :)

R.