Scope (NISO JATS table model)
Specifies the cells for which the current <td> element or <th> element provides header information. Screen readers and other Assistive Technologies use @scope to provide information about the table structure that would be obvious to most sighted people. (This attribute is based on the XHTML scope attribute.)
The @scope attribute applies to both <td> or <th> since, for example, a table cell in the first column may act as a label (header) for the other cells in the same row. The values for @scope are keywords, which provide an alternative to describing the header by naming header elements explicitly (Using @headers on a <th> or <td> element).
The following graphic shows the scope of the different scope values. The figure and the value table below apply to a table in which columns progress from left to right. In a table in which the columns progress from right to left, the effect is down and/or to the right instead of down and/or to the left.
@scope is based on and intended to be converted easily to the XHTML “scope” attribute. It also maps to the “Scope” attribute in Tagged PDF.
In HTML 4.01, scope applies to both <td> and <th> elements. In HTML5, scope applies only to <th> elements. When scope is not specified, the ‘missing value default’ in HTML5 is ‘auto’, where the scope is determined based on context: in short, a <th> element is automatically a column header if there are no <td> elements in either the rows spanned by the a <th> element or any preceding rows, and it is automatically a row header if there are no <td> elements in either the columns spanned by the a <th> element or any preceding columns. A <th> element may, therefore, automatically be both a column header and a row header.
The @scope attribute in Tagged PDF has values for “Row”, “Column”, or “Both”. Scope applies only to the TH structure element, so a <td> with a scope attribute must be tagged as TH in the PDF. However there is no harm in tagging a <td> as TH since the usual visual differences between <td> and <th> elements are not relevant to a screen reader. Scope was added in PDF 1.5. Up to and including PDF 1.7, there was no automatic Scope assignment. PDF 2.0 assumes that the TH in the first row and column has a Scope value of ‘Both’, that other TH(s) in the first row have a value of ‘Column’, and that any other TH in the first column have a value of “Row”.
|col||Acts as a header for cells in the same column in following row.|
|colgroup||Acts as a header for cells in the current colgroup that are down and to the right of the current cell (i.e., the remaining cells named in the <colgroup> element).|
|row||Acts as a header cell for cells in the same row in following columns.|
|rowgroup||Acts as a header cell for cells in the current row group (i.e., in the current <thead>, <tfoot>, or <body>) that are down and to the right of the current cell.|
|Restriction||@scope is an optional attribute; there is no default.|
@scope attribute showing row groups:
... <table-wrap position="float" orientation="portrait"> <caption> <title>Measurement of legs and tails in Cats and English speakers</title> </caption> <table> <thead> <tr><th>ID</th><th>Measurement</th><th>Average</th><th>Maximum</th></tr> </thead> <tbody> <tr><td/><th scope="rowgroup">Cats</th><td/><td/></tr> <tr><td>93</td><th scope="row">Legs</th><td>3.5</td><td>4</td></tr> <tr><td>10</td><th scope="row">Tails</th><td>1</td><td>1</td></tr> </tbody> <tbody> <tr><td/><th scope="rowgroup">English speakers</th><td/><td/></tr> <tr><td>32</td><th scope="row">Legs</th><td>2.67</td><td>4</td></tr> <tr><td>35</td><th scope="row">Tails</th><td>0.33</td><td>1</td></tr> </tbody> </table> </table-wrap> ...