page-sequence--a major part (such as front or body) in which the basic page layout may differ from other parts
flow--a chapter- or section-like division within a page-sequence
block--a paragraph (or title or block quote, etc.)
inline--e.g., a font change within a paragraph
wrapper--a "transparent" object usable as either a block or inline object that has no effect other than to provide a place to hang inheritable properties
list FOs--list-block, list-item, list-item-label, list-item-body
graphic--references an external graphic object
table FOs--mostly analogous to the standard (CALS, OASIS, HTML) table models