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@longdesc = programmatically determinable

Tuesday, 24 August 2010

With @longdesc the relationship between an image and its long description can be programmatically determined. I think this is one of the best arguments in favour of this attribute. This is because the tendency in HTML has been towards higher degrees of semantics and programmatically determinable relationships, for example:

• before HTML 4, form fields could not be associated with labels because HTML had no label element; HTML 4 introduced the label element and a mechanism to associate labels with form fields in a way that can be programmatically determined;
• before HTML 4, table data cells were not explicitly associated with header cells; HTML 4 added @id and @headers to TD and TH elements to enable explicit association;
• before XForms and HTML5, there was no way to mark form fields as required, so developers resorted to JavaScript behaviours to work around this;
• before XForms and HTML5, there was no way to define data types for form fields, so developers resorted to JavaScript behaviours to work around this.

The list can probably be expanded, but the point should be clear: not adding @longdesc to HTML 5 is a step backwards because it goes against the tendency to more semantics and programmatically determined relationships.