The <abbreviated-form> element represents a reference to a term
that might appear in an abbreviated form (often an acronym). The long and short forms
term are generally defined in a <glossentry> topic. Processors display
the referenced term when rendering an <abbreviated-form>
The <glossref> element is a convenience element in maps for
creating a reference to a glossary topic. It has a required @keys attribute, which
forces the author to create a key by which inline terms can reference their definition.
when <glossentry> topics are used to define acronyms, this reminds authors to
create a key which <abbreviated-form> elements can use to reference the short
and expanded versions of that acronym.