Difference between absolute yeild spread and nominal spread

Schweser says: Absolute Yield spread: Quantifies the difference between nominal yields on two bonds or two types of bonds. Calculated by: Absolute yield spread = higher yield - lower yield Nominal spread = issue’s YTM - YTM of a Treasury security with similar maturity. My suspicion is that the nominal spread is a “type” of absolute yield spread i.e. it’s the absolute yield spread formula with a treasury security substituted as the lower yield spread (kind of like the sfr ratio is a type of roys safety first ratio, just substituting in the rfr for the target rate). Anyone agree?