Focus on "forces the context of the _expression_ that results in that
argument into array mode" (or "forces calculation of the argument's
_expression_ into non-scalar array mode" as ODFF states).
Best some example:
Cells A1:A3 := {-1,-2,-3}
SUMPRODUCT(ABS(A1:A3))
results in 6 because it forces array context on the _expression_
ABS(A1:A3), where ABS() expects a scalar value and without array context
would take the implicit intersection of the formula cell's position and
the range A1:A3 and return one single value. In array evaluation context
it iterates over the values A1:A3 and returns an array of results.
