Chinese characters may be more complicated than latin letters, but they can express in two or four ems what might take two or four words in English: a little taller but much shorter.
So when faced with making tables where space is a premium, Chinese (and Japanese and Korean) writers and layout-ers naturally made use of these characteristics to allow denser tables. Chinese (and Japanese and Korean) itself is traditionally written with a grid too, which could themselves be considered a kind of table.
There is almost no recognition of these unusual Chinese table forms. For the last decade, there is, it is true, more support for some basic features (such as simple diagonal header split) in some mainstream word processor products, but in general there is little awareness. (Indeed, sometimes application developers actually turn off some Asian features in the Westerner versions of the software, even though the feature may be useful, to avoid the perception of bloat. FrameMaker used to do this for ruby text, I recall.)
You can see a request made for this kind of feature into OpenOffice at Diagonal Table Header Specification (ODF). But the kinds of features asked for there are just the thin end of the wedge, comparted to the richness of Chinese tables found in the hand-laid out tables.
One of my projects at Academia Sinica in Taiwan involved going through archives of Chinese printed books to find characteristic examples of Chinese tables. I used to have a website with dozens of scans of examples, but it has been taken down. I thought I would put some of the images that were saved in the Wayback Machine, by way of partial rescue.
(If this material looks familiar, I have previously put one of these diagrams in a blog item: Standardization as a collective failure of imagination)
Diagonal and Kite HeadersThe first example is where the small size of Chinese characters makes it possible to collapse several rows of headers into a single upper left box.
This example is unusual, because it actually uses English words, so we can get a really good idea of what the function of the subcells are. You can see that, graphically, it is not a good fit for English: it would presumably be worse with a language with even longer words, such a German!
You can see that the split cell contains titles for 1) the top header row, 2) the body of the table, 3) the subheaders in the second column, and 4) the headers in the first column. You can see also the kite shape of 2) which intrudes into 3). This is some graphical license, but the kite shape is very typical.
(If you want to see the whole graphic, right click and your browser probably has a "Show Image" item on the pop-up menu. Then use the back button to return to this page.)
The following example is a much simpler kind of diagonal split-cell header. Its connection to the top row should be clear.
Diagonal Data Cells
Not only headers may be split diagonally. Here is some data results. It seems that in this case the diagonal split is used to indicate that the data items in the cell are connected to each other. This is a semantic which seems missing from the vocabulary of Western tables. You can see it has a diagonal split header left botton, that matches the data items.
This kind of table has a graphical structure that we would perhaps more associate with a form rather than a table.
Finally, here is a very messy and repellent diagram. (If I remember, it was an old Taiwanese table assigning bopomofo letters to buses or trains for particular routes.) But rather than sneer, we should ask ourselves what graphical/writing problem is this layout solving?.
In this case, we have a basic table with three header rows and three header columns. And we have a split cell to give a label for the first two header rows and a label for the first two header columns. Then we have another split cell, giving labels for the third column headers and third column rows. Try doing that without split cells!
In the markup world, we have been living in and perpetrating a graphically impoverished set of technical capabilities. This started early, with the OASIS CALS Exchange Table Model, where vendors, in order to get better interoperability, agreed to remove from the data format features that were not common. The CALS model has in turn highly influenced HTML (and even ODF and OOXML): the exchange subset becoming in effect the last word in what tables are supposed to be.
For some more info on ways to view these, you might also check out my old pages at Academia Sinica: Chinese Tables and Split Cells. It is a shame that the more extreme examples of Chinese tables have gone AWOL: some are more like little diagrams than what we conventionally think of as tables. We Westerners are of course allowed to think that these things are mad, funny, quaint, interesting, horrifying, etc: everyone is allowed to think that of a foreigner's culture: but I think we should be careful not to dismiss the usefulness of these idioms for CJK use, and even for our own use.
On the subject of Internationalization, there are of course other sources for requirements floating about, particularly as China is regaining its voice: as well as impacting CSS, it will also impact OOXML and ODF (which themselves can act as rich sources for formatting ideas for CSS.) One of the particular sources of information, outside the W3C, on Chinese requirements is the scanty details that can be gleaned about China's UOF format in English. There is a document UOF Translator Requirements on a Sourceforge UOF-OOXML translator project, and a document Comparison Document for the ODF to UOF translator project.
Update O'Reilly's formatting goblin's don't like ASCII art formatting for reader comments, so I am putting in some of the table from Maria's comments below.
| | Variable Group A |
| | subgroup a | subgroup b |
row header 1 | row header 1.1 | data 1.1.a | data 1.1.b |
_____________| row header 1.2 | data 1.2.a | data 1.2.b |___