How common is it that employers allow this? At my current job (in a mix of healthcare/academia) I can open source anything I want. In my previous job, not only

How common is it that employers allow this? At my current job (in a mix of healthcare/academia) I can open source anything I want. In my previous job, not only couldn’t I open source anything, I was forbidden to use any open source code or even post questions on sites like SO (for fear it might reveal something about our operations).