I find that contractual language covering "ownership" of IP is likely ineffective and doesn't match reality. If I'm paid by a company to write some code while employed, sure the employer owns it. But it also exists in my brain. Do they own that too? Can I write it again for myself or for another employer? If not, how much needs to change? If I wrote it in Python originally, would a functional equivalent in JavaScript remain "owned" by the original employer? I'm surprised contract disputes surrounding this concept aren't quite common.