What feature allows a baffled tank to control forward-and-backward surge while still holding one continuous volume of cargo in that compartment?

49 CFR 383.119(c); AAMVA CDL Manual Section 8.2.4, "Baffled Tanks," p.8-8-2

Understanding that baffles work by letting liquid pass slowly through holes, rather than blocking it entirely, explains why baffled tanks still allow some side-to-side surge even though forward-and-back surge is reduced. That nuance is exactly what the manual flags as a residual rollover risk.