Ask HN: Technical/Code Validation as part of an investment round.

Hi all, My startup is actively pursuing seed investment, and I was wondering about technical/code validation as part of due diligence. Is it standard practice for code to be examined by a third party prior to investment being made? I would imagine in biotech, green tech, clean tech, etc that it would be fairly standard to get the core technology validated by independent experts. But is this normal for a strictly software startup? If placed in this position, what sort of protections should be put in place to protect both parties?