Section 3.25 URLs and External References
<url>tag always requires an
@hrefattribute. Usually this will be a complete address for some external web page, or other external resource. The
@@visualattribute is sometimes mandatory, but sometimes optional. It should provide a simplified version of the URL for use in print, or similar situations. Finally, you can provide content for the
<url>element, which will become the clickable text in most realizations.
<url>element is empty (no content), then the value of the
@hrefattribute or the optional
@visualattribute will be the link text, with a preference for the latter. When you instead provide content, you can use PreTeXt elements much like any other piece of text that would occur in a paragraph. In this case, a
@visualattribute is now highly recommended, as an alternative to the content, providing information about the actual URL for non-electronic formats like print. A default version of the value of the
@hrefattribute will be used in its absence. This visual version of the URL will appear in a footnote.