Qasr restricts a property or attribution to a specified term. The maqsūr is what is restricted, and the maqsūr ʿalayh is what it is restricted to.
In a suitable contrastive context, «fī al-dāri Zaydun» can treat being in the house as an attribution confined to Zayd among those in view. It does not state that Zayd has no other properties or could never occupy another location.
ConceptMeaning
Predicate-frontingPlacing the predicate first
RestrictionLimiting an attribution within a contrast
Prominence aloneForegrounding without exclusivity