There will be a nice accompanying doc to go with XFUEL but for now I'll state a couple comments.

XBY is and will always be the lifeblood of creating modules within the core platform. Any modules or applications built on the XBY platform uses XBY, NOT XFUEL.
This is achieved through the DICOM API

XFUEL IS;
Proof of Tech (PoSign) working on the XBY Platform
First token available on the X-CHANGE utilizing XBY Core (xby/xfuel pairing)
Can be used in partial paying for a STATIC
Used for paying Dev's


Thanks
BRYAN_K