Bowing In The Sanctuary

[Nihil Obstat]

I was just reading a short thing that mentioned that we always bow towards the altar rather than the tabernacle. (Including at any times when they may be crossing between the altar and tabernacle.)
Makes perfect sense to me, but I wanted to clarify that this is indeed the case.
Also does this apply only during mass, or also before and after, if the Eucharist was in the tabernacle.

A further question: at what points in the mass is it appropriate for anybody except the priest to cross behind the altar? Is it ever permitted? How serious a mistake is it if someone crosses behind the altar at an innapropriate time?

[cappie]

From the General Instruction of the Roman Missal:

274. A genuflection, made by bending the right knee to the ground, signifies adoration, and
therefore it is reserved for the Most Blessed Sacrament, as well as for the Holy Cross from the solemn adoration during the liturgical celebration on Good Friday until the beginning of the Easter Vigil.

During Mass, three genuflections are made by the priest celebrant: namely, after the showing of the host, after the showing of the chalice, and before Communion.

If, however, the tabernacle with the Most Blessed Sacrament is present in the sanctuary, the
priest, the deacon, and the other ministers genuflect when they approach the altar and when they depart from it, [b]but not during the celebration of Mass itself.
[/b]
Otherwise all who pass before the Most Blessed Sacrament genuflect, unless they are moving in procession. Ministers carrying the processional cross or candles bow their heads instead of genuflecting.

There is no mention of the practice of passing in front of the altar vs passing between altar and tabernacle.

The GIRM (n. 298) reminds us of the ancient tradition of seeing the altar as representing Christ, the Living Stone (cf. 1 Peter 2:4). Because of this association, a bow of the body is prescribed as the normal gesture made toward the altar, as if toward Christ himself. In particular, all the ministers bow toward the altar when they arrive at the sanctuary at the beginning of Mass and at the end of Mass, before leaving the sanctuary.