Validatation of slug values

[nschonni]

Currently there was one case of invalid values crashing the parser as discussed in mdn/content#329 (comment)

My 2 cents is that is should probably be an allow-list following the URL RFC like https://stackoverflow.com/a/1547940/455535 rather than a deny-list of characters.

There is probably a separate discussion needed for valid file paths so that the repo can be checked out on both unix and Windows filesystems

[Ryuno-Ki]

Sounds like a good idea.
I'd vote to ban at the very least Unicode confusables.