Qubes-vmm-xen-stubdom-legacy

Do someone have some lore about GitHub - QubesOS/qubes-vmm-xen-stubdom-legacy ?
It seems it download an even older version of xen and everything and apply some custom patch.

There is already GitHub - QubesOS/qubes-vmm-xen: Qubes component: vmm-xen to compile xen
and GitHub - QubesOS/qubes-vmm-xen-stubdom-linux to compile the stubdom.
So i am a little bit confused about it.

What is qubes-vmm-xen-stubdom-legacy ? why is it needed ? (found no documentation mentionning it)