Table header

[Svante Schubert <svante.schubert@gmail.com>]

I got a question on table header. Especially from ODF implementors I would like to know about their application behavior for headers.
(The XML for header is similar for rows and column. In the following I will only mention columns.)

Let me start with a quick summary on the XML of table columns:
The most inner element of columns aside the content is the single <table:table-column> element.
The most outer (optional) element of columns is the <table:table-column-group>, which can be nested in itself and its only purpose is for hiding a group of columns via its boolean @table:display attribute.

Within these <table:table-column-group> there might be single columns (ie. <table:table-column>), but as well two further groups: <table:table-columns> and <table:table-header-columns>

Columns grouped by <table:table-header-columns> are repeated on a next page, if the table is too large for one page.
Columns grouped by <table:table-columns> are NOT on a next page, if the table is too large for one page.

What troubles me, is the definition of table header column
http://docs.oasis-open.org/office/v1.2/cos01/OpenDocument-v1.2-cos01-part1.html#element-table_table-header-columns
as a single group of header columns.
"A table shall not contain more than one <table:table-header-columns> element, except that the table contains grouped rows defined by one or more <table:table-column-group> 9.1.10 elements. In this case, the table and each distinct group may contain one<table:table-header-columns> element, if and only if the table columns contained in the <table:table-header-columns>elements are adjacent."
In other words ODF allows only one or a connected group of headers. Its position is arbitrary.

Following problems:

1. Currently the ODF schema is not restricting the uniqueness of a header (group), although I believe this is possible.
   
2. table:table-columns seems to be a redundant element as none repetition should be the default.
   
3. Why is the header not mandatory first in the table?
   Is anyone aware of an table application (not necessary an ODF application) that is able to have header in arbitrary places?
   And if headers can be on arbitrary positions, what would be the position of the header on the next page? The first, similar position as on the first page or last position?
   

PS: Perhaps someone might pick it up as a scenario for the ODF Plugfest in Gauda. I have a colliding family event and will not be able to attend.

Regards,
Svante