function _isSpecialCommand(commandID) {
        if (brackets.platform === "mac" && commandID === "file.quit") {
            return true;
        }

        return (_specialCommands.indexOf(commandID) > -1);
    }
@private

Checks whether the given command ID is a special command that the user can't bind
to another shortcut.
@param {!string} commandID A string referring to a specific command
@return {boolean} true if normalizedKey is a special command, false otherwise.