The PICO-8 built-in editor supports up to 8 tabs. These are represented in the .p8 file as a single Lua code block delimited with -->8 comments. If I am editing the .p8 file with an external editor but still want to establish tabs for the internal editor, I add -->8 comments manually. If I add more tabs than the internal editor can handle (8 or more delimiters), code beyond the 8th tab is ignored.

It's a pretty edgy edge case to want both external editing and tabs for the internal editor, but I found this behavior surprising enough that I humbly request a tad more thought to it. I would agree that evaluating code that isn't displayed in the internal editor is not the right fix, nor is adding UI to support unlimited tabs. My preference would be to fail to load the file as if it didn't parse, with an explicit error message, or just consider everything beyond the 8th tab as part of the 8th tab.

I think considering everything after the last tab to be appended (along with the -->8 markers) is the most natural solution. I've also added 8 more tabs for 0.1.12d, so it will be even more edgy, but still worth handling nicely.