[yocto] Yocto recipe license

[Contrib Open Source]

Hello,

it seems that license.manifest file describes application/lib/etc.
source code license,
but what about Yocto recipe license itself ?
So what is the license of a Yocto recipe ?
How to know it ?
If a Yocto recipe is GPL2, and we extend (*.bbappend) this recipe,
does contamination effect applies to the extented recipe ?

Thanks for your help,
contrib