Easily I can think you hundreds of books where the author set "Preface", "Forword", "List of Abbreviations" and "List of Content" in a subordinate style. When the main text starts, this style is the same that is used for the second (or third) sectioning level. The same shows up in TOC: if these entries are listed in TOC, they are visually structured (by indentation and font) explicitly as the second (sometimes third) sectioning level.
As far as I have understood Hans' answer, the logic for bookmarks (or structured, tagged PDF in general?) works differently: even though the "design" of these sections (ie. section *headings*!) by the author is intended to be subordinated, nevertheless these section should be structured in a parent/child way: the first section mentioned is meant to be the highest level:
Would this map and represent the structure that the author was thinking of?
In a typeset toc it's often quite clear as visual clues are used (indentation, font, vertical spacing, either of not a pagenumber) I have made some quite complex structured docs (tens of different heads at the same level). This goes ok as long as one is in control, but in automated flows with input that can have some components not being present and then also typeset one can have interesting confusing situations. In such cases fonts/spacing in a toc depend on an analysis of the structure (runtime). Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com | www.pragma-pod.nl -----------------------------------------------------------------