Two question marks supplying a fallback for an absent value.
Two question marks yield the value on the left unless it is absent, in which case they yield the value on the right. It differs from a plain or in treating zero and the empty string as present.
ECMAScript defines the doubled question mark as producing the right-hand value only when the left-hand one is null or undefined.
Contexts: Software
The distinction from a logical or is the point of the operator: an or would replace a legitimate zero or empty string with the fallback.
Contexts: Software
Two identical hooked strokes side by side, each curling from left to right above its own dot.
Both are built from lines and dots, and both are used in software contexts.