The collection is made of a series of nested collections, grouping body row templates into logical structures. It is first grouped by the logical row the template appears in, then by the sections of templates which interleave child groups, then by the templates of each section, and finally by the logical column the template appears in.
Usage:
It is important to note that both the value and range of the column index here does not correspond to an item's column index, as the body row includes templates for the row header and row footer as well if they are visible. The body rows collection also stores references to blank template instances used as place-holders when the template that would appear in that position is hidden, or an item at that particular coordinate does not exist.
For example, the 5th item's 2nd body template after the 1st child group in a non-wrapped vertically repeating
group with no row header is