Slash in filename?

[nbrege]

I have an issue that's been driving me nuts for a couple hours now. I am working on developing a front end interface for yt-dlp, which is an open-source command-line downloader for sites like YouTube. I am successfully downloading all the songs (currently over 600) in a YouTube Music playlist to my PC. I have yt-dlp configured to name the file as "Artist - Title.mp3". The problem is that if a track has a slash ("/") in the title the file actually gets saved with the slash in the filename. Since a slash is a forbidden character in a filename, I am at a loss to understand how yt-dlp can write such a file. Doing some Googling I found that yt-dlp supposedly replaces any illegal characters (<>:"/\|?*) with the unicode equivalent, but the slash in these files looks like a regular forward slash. I wrote a test routine that loops through the characters in the filename & it says that the slash is ascii 63, which is a question mark. Also, any track titles that have a question mark in them DO get written with a unicode question mark character. Anyone have any idea what this slash character is & how it's able to be used in a filename?

Example of files with question mark & slash in filename:




Here is the same file with the slash that I manually replaced with a unicode slash: