Fantastic, thank you!
A first test was successful, but I'll try it thoroughly tonight, both on my phone and Rockbox. This makes stuff so much easier! <3
[Edit]
I've tried loading the "new" playlists on VLC for Windows, Linux and Android, my Rockbox player (Sansa Clip Zip), Linux Mint default movie player "celluloid" and my favourite Linux music player "Exaile". They all successfully loaded the playlist!
Thank you very much, these changes finally allow me to create playlists and just copy them everywhere, instead of having to edit every single one of them first!
[Edit 2]
Ok, found a little issue with Rockbox, but I can live with that: Rockbox prefers the format to be UTF-8-BOM with LF line endings (.m3u8), otherwise it won't load files with exotic characters, e.g. cyrillic. Rockbox doesn't support PLS and EXTM3U doesn't make a difference, but I think it's actually the byte order mark.
[Edit 3]
I found out that Rockbox is completely happy with XMPlays .m3u files, if I just rename them to .m3u8 - no BOM or line ending conversion necessary!
Ian, could you possibly adjust the M3U save dialog filter to show .m3u8 files, too? That'd make things even more comfortable.
As always, thanks for your effort!