Under Hiding, on p. 142 of YS, it references situational modifiers as being on p. 214, there are no situational modifiers on this page, just other skills complementing or restricting...which is a somewhat different thing.
If circumstances on their own are intended to be allowed to complement or restrict a skill, that would make sense and be an elegant way to handle it, but that's not stated anywhere I've found, and certainly not on p. 214.
On an entirely different note Carlos Ramirez on p. 214 of Our World appears to have split a Refinement between getting an Item Slot, and an Evocation Specialty (normally a Refinement gives you two of one of those things). As far as I know, that's not legal. If it is, it should probably be mentioned in some marginalia near Refinement. Luckily, there's not much there currently.