Question on Condition (/;)

Question

Condition has attribute HoldAll which prevents evaluation of its first argument before applying the Condition. But for some reason C

Answer 1

Condition use often depends on what is in the left hand side, so it must evaluate the LHS at least to some degree. Consider:

MatchQ[3, a_ /; IntegerQ[a]]

   True

p = {a_, b_};

MatchQ[{3, 0.2}, p /; IntegerQ[a] && b < 1]

   True

Both for this and from this, I would have guessed that Condition had attribute HoldRest rather than HoldAll. It probably needs HoldAll for some internal use, perhaps related to the SetDelayed usage.