Return generated details for a caption.
The identifier which is returned must be consistent with the
fragment which would be generated by function (href-to) in
the HTML stylesheet. This is satisfied by returning simply the
element's ID.
An element (typically the
TABLE or FIGURE element the caption is a member of)
which has an ID attribute, and which will be used to generate the
caption reference.
Type: list of strings
A list containing, in order,
the caption legent (eg, `Fig. 1.3'); the caption number as a string (eg,
`1.3'); either a unique identifying string
which is usable as a link target, or #f if the element's ID attribute
is implied. The figure/table number is returned separately so it
can be put to different uses (eg, as an entry in a list of figures).