"Ready to build Qty" uses all on-hand or only available on-hand?

From "Using Supply Planning" manual, 25c: "The Ready to Build Quantity value of a supply order represents the quantity of the supply order that can be built using only on-hand supplies of components."

Can someone clarify if by that they mean it uses "all on-hand" inventory? Or only the "available on-hand"? My question is if part of the on-hand is already commited to another WO, will the component appear as available in the "Ready to use Qty" value?