it is not official so you have to put it within passthrough. I use layout in order to be able to access resources like hydrogen drumkits or Soundfont2 files. These files are stored in:
/usr/share/hydrogen /usr/share/sounds
Currently I include hydrogen-drumkits and fluid-soundfont-gm/fluid-soundfont-gs in my snap. Without layout I can’t access the /usr subdirectory.
But as using it I am able to open the provided wav, flac and sf2 files located in /usr subdirectory. Else I would get permession denied within GtkFileChooserDialog.