What is the Mime type to display notifications?

I want to replace the ubuntu notification box. What I mean by “notification box” is the little popup that shows up when I change my music on spotify, for example. From what I can tell the OS receives a message with the information and uses Mimeinfo.list to know which program to call and display that message.

Now, I already did some changes with this in the past. Like pointing


I’m looking at the Mimeinfo.list file to try and point the message types from the default to my current program like in the example above, but I have absolutely no idea what type refers to the notifications. Anyone knows what is it?