Nostalrius Begins - Quality wow vanilla realm (1.12)

I am wondering if it is legal to use multiboxing to level up two characters at the same time from level 1? (for example a priest and a hunter) without the use of any third party software to help? I kinda want to level up two characters at a time, and I have found the rule set on multiboxing very vague and I don't want to take any risks. Not power leveling one character, just normal leveling two characters wich I alt-tab between.

Is that useage of multiboxing legal? ( I would prefer an answer from a gm).