Groups allow segments to be addressed relative to the same frame address. When LINK encounters a group, it adjusts all memory references to items in the group so that they are relative to the same frame address.
Segments in a group do not have to be contiguous, belong to the same class, or have the same combine type. The only requirement is that all segments in the group fit within 64K.
Groups do not affect the order in which the segments are loaded. Unless you use class names and enter object files in the right order, there is no guarantee the segments will be contiguous. In fact, LINK may place segments that do not belong to the group in the same 64K of memory. LINK does not explicitly check that all segments in a group fit within 64K of memory; however, LINK is likely to encounter a fixup-overflow error if this requirement is not met.