Since the relationship between <group> and <text> is quite similar to that between <text> and <div>, we sometimes encounter situations where we could use either <text> or <group>. We apply the following criteria:
--if the interior chunks have been, or could be published separately, use <group> and <text>. So a trilogy should be encoded as <group> with its component novels as <text>. A novel published serially in three separate volumes might also be a <group>.
--similarly, if the interior chunks have their own front and/or back matter, use <group> and <text>.
--if the interior chunks could not be imagined as separate publications, use <text> and <div>. So the chapters of a novel should always be <div>.
Some of the most difficult cases to decide involve textual units such as poems or essays, which possess an ontological independence and distinctness, and may be published separately or as part of a collection of which they are an integral part. In general, we treat collections of poems, essays, and letters as <text>-level items, with the individual poems, letters, or essays encoded as <div>. The rationale here is that these items are collected together not as independent units but as part of a published whole that has a shape and an internal ordering structure. Although each poem or letter has an ontological separateness as well, we want to emphasize their function as part of the larger whole. While we could accomplish this using <group>, there seems to be no advantage to this approach, since these items do not have any front or back matter (otherwise we would have encoded them as <text>).