The CSS table model is based on the HTML4 table model, in which the structure of a table closely parallels the visual layout of the table. In this model, a table consists of an optional caption and any number of rows of cells. The table model is said to be «row primary» since authors specify rows, not columns, explicitly in the document language. Columns are derived once all the rows have been specified — the first cell of each row belongs to the first column, the second to the second column, etc.). Rows and columns may be grouped structurally and this grouping reflected in presentation (e.g., a border may be drawn around a group of rows).
Thus, the table model consists of tables, captions, rows, row groups (including header groups and footer groups), columns, column groups, and cells.
The CSS model does not require that the document language include elements that correspond to each of these components. For document languages (such as XML applications) that do not have pre-defined table elements, authors must map document language elements to table elements; this is done with the ‘display’ property.
This chapter defines the processing model for tables in CSS. Part of this processing model is the layout. For the layout, this chapter introduces two algorithms; the first, the fixed table layout algorithm, is well-defined, but the second, the automatic table layout algorithm, is not fully defined by this specification.
For the automatic table layout algorithm, some widely deployed implementations have achieved relatively close interoperability.
Table layout can be used to represent tabular relationships between data. Authors specify these relationships in the document language and can specify their presentation using CSS 2.1.
In a visual medium, CSS tables can also be used to achieve specific layouts. In this case, authors should not use table-related elements in the document language, but should apply the CSS to the relevant structural elements to achieve the desired layout.