Contribution to Qt Creator
While consulting on Qt, I was working on multiple projects at once, and one of them had tab expansion turned off (my preference is to always expand tabs). At that time, Qt Creator did not have the ability to maintain per-project tab expansion settings.
I made an enhancement to Qt Creator to help me deal with this – I added an option to automatically infer tab expansion based on the surrounding code.
My contribution was enhanced by other contributors and eventually became the ‘Mixed’ option under Settings > Text Editor > Behavior > Tab policy.