Like almost everyone here, I have a handfull of scripts and software that I have developed and am enthused about. I will be looking for my first job as a software designer / coder. It seems natural that I will be eager to please my employer and use scripts or similar methods that I have developed and worked for me in the past to please my employer. It seems certain that many things that I code will look very similar to things I have coded in the past.

I don't understand how to document and articulate to an employer that this code base was mine before I got here and this will continue to be mine when I leave. Surely, this is a common issue, but none of the various searches I've done on the net have produced an answer to this question. How is this situation commonly dealt with in the industry?

I feel like there should be a digital version of sending myself a 'certified letter' with my code/software/scripts contained. I'm not trying to protect my code from others using it; I am trying to protect my right to continue using my code base that I have developed prior to to gaining employment with an employer.