Beam objects by default do not need to have priorities specified. However, beams have an option to be meshed "Mesh as Slab" using the priority method. Any beams using the priority method will be meshed first along with slab and opening areas. The remaining beams are meshed last and are merged with the elements that result from the mesh resulting from the priority method. Any "gaps" between the beams and other meshed surfaces are filled during the process, although this will result in a warning.

Slab, beam and opening objects defined in the Mesh Input Standard Plan

The Element Slab Summary Plan after mesh generation from the previous figure.