Description of and pointer to an external file containing a still image.
Any combination of:
<alt-text> Alternate Text Name (for a figure, etc.)
<long-desc> Long Description
Linking Elements
<email> Email Address
<ext-link> External Link
<uri> Uniform Resource Identifier (URI)
<object-id> Object Identifier
<label> Label (of an Equation, Figure, Reference, etc.)
<caption> Caption of a Figure, Table, etc.
<attrib> Attribution
<permissions> Permissions