When modularizing documentation, it is sometimes necessary to create empty modular elements whose content will be supplied during the assembly process. For example, a chapter might not need any introductory paragraphs and so just begin with the first section. If the chapter and sections are all in modular files that are put together with the new assembly element, then the chapter should contain only a title (and other info elements). However, such a nearly empty chapter does not currently validate, because a chapter must have either block content or sections (or both). To better support modularity, a chapter should be permitted to be empty of content. The same is true of appendix, preface, section, and topic.
I propose that the content models be modified in 5.1 to allow for nearly empty elements.