spark/core-firmware — pull request #243 by ScruffR (2014-07-28 09:59:08+00:00)
Title: Wiring compatibility:

As discussed with @BDub in this old thread of mine (https://community.spark.io/t/digitalwrite-in-compatibility-with-arduino/3755).

Wiring treats everything but LOW as HIGH (just like "if" treats everything but 0 as true)