While it is possible to build a simple table quickly, complex tables with varying border styles, running headers and footers, and column-based layout were not easily constructed from the old HTML 3.2 table model. Microsoft rectified this inadequacy somewhat by adding a number of table-layout controls to Internet Explorer version 3.0. These very useful extensions found their way into the HTML 4 standard and subsequently into XHTML. They provide row-based grouping and running headers and footers, along with column-based layout features.
Within tables, all rows are created equal. In real tables, some
rows are more equal than others. And most tables have header and
footer rows that repeat from page to page. In large tables, adjacent
rows are grouped and delineated with different rule lines to make the
tables easier to read and understand. HTML 4 and XHTML support all of
these features with the
<thead> tag to
define a set of table header rows. The
<thead> tag may appear only once per
table and is placed at the beginning, just after the
<table> tag. Within the
<thead> tag, you may place one or more
<tr> tags, defining the rows
within the table header. If given the opportunity, the HTML 4/XHTML-compliant browser replicates these heading rows when the table is printed or displayed in multiple sections. Thereafter, it repeats these headings on each printed page if the table appears on more ...