Description of and inline pointer to an external file that provides supplementary information for the document.
Any combination of:
Text, numbers, or special characters
<alt-text> Alternate Text Name (for a figure, etc.)
<long-desc> Long Description
<email> Email Address
<ext-link> External Link
<uri> Uniform Resource Identifier (URI)
<bold> Bold
<italic> Italic
<monospace> Monospace Text (Typewriter Text)
<overline> Overline
<roman> Roman
<sans-serif> Sans Serif
<sc> Small Caps
<strike> Strike Through
<underline> Underline
<named-content> Named Special (Subject) Content
<styled-content> Styled Special (Subject) Content
<sub> Subscript
<sup> Superscript