The .. range operator is really two different operators depending on the context. In a list context, it returns a list of values counting (by ones) from the left value to the right value.

In a scalar context, .. returns a Boolean value. It is false as long as its left operand is false. Once the left operand is true, the range operator stays true until the right operand is true, after which the range operator becomes false again. The right operand is not evaluated while the operator is in the false state, and the left operand is not evaluated while the operator is in the true state.

The alternate version of this operator, ..., does not test the right operand immediately when the operator becomes true; it waits until the next evaluation.