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10.7. Tables

Perhaps as a result of a generic need to be able to describe table layout -- something CSS1 lacks -- CSS2 includes a handful of features that apply directly to tables and table cells. First, there are 10 new table-related values for display:

table
inline-table
table-column-group
table-column
table-row-group
table-row
table-cell
table-caption
table-header-group
table-footer-group 

While the effects of most of these are obvious from their names, at least two may not be familiar to you. table-header-group and table-footer-group are used to mark the header and footer of a table. These are displayed, respectively, above or below all the rows of the table, but not outside of the table's caption.

Another interesting effect is that you can align text on a character by using the text-align property. For example, if you wanted to line up a column of figures on a decimal point, you might declare:

TD { text-align: "." }

As long as a set of cells are grouped into a column, their content will be aligned so that the periods all line up along a vertical axis.

Far from relying on existing properties, CSS2 provides a whole array of brand-new properties in the table section. Here are a few of them:

There are also properties describing how visibility and vertical-align are applied to tables. There is also a caption-side property, which functions exactly the same as the ALIGN attribute on the <CAPTION> tag, and the property speak-header-cell, which controls how header cells are handled by speech-generating browsers (more on that later).



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Figure 7-19

Figure 7-19. Negative margin

Negative percentages are also permitted. These will behave like any negative length value, with the obvious difference that the amount of negativity will depend on the width of the parent element. Thus:

P {margin: -10%;}

Figure 7-20 illustrates the consequences of such a rule, where the amount by which paragraphs overlap each other and spill beyond the browser window is entirely dependent on the width of that contains five list items:

LI {margin-top: 10px; margin-bottom: 15px;}

Thus, each list item has a 10-pixel top margin and a 15-pixel bottommargin. However, when the list is rendered, the distance betweenadjacent list items is 15 pixels, not 25. This is because along thevertical axis, adjacent margins are said to be collapsed. In otherwords, the smaller of the two margins is eliminated in favor of thelarger. Figure 7-16 shows the difference betweencollapsed and uncollapsed margins.