What is the provenance of .gtkrc-xfce?

I'm currently setting up a Linux Mint 21.3 Xfce Edition installation, and part of that is tidying up the dotfiles in the home directories. There aren't that many that can be moved in the base installation, and xdg-ninja has been a great help, but it does not have anything to say about one dotfile: .gtkrc-xfce. I've tried searching around on the internet and there are currently no obvious results for it in [the GTK documentation](https://duckduckgo.com/?q=gtkrc-xfce+site%3Adocs.gtk.org) or [the Xfce documentation](https://docs.xfce.org/start?do=search&id=start&sf=1&q=gtkrc-xfce) . Where has this dotfile come from? Is there a way to get it to respect the XDG base directory specification?