unique, these are the literal <literal>schema</literal> or
<literal>element set</literal> names used in
<ulink url="http://www.loc.gov/standards/sru/srw/">SRW</ulink>,
unique, these are the literal <literal>schema</literal> or
<literal>element set</literal> names used in
<ulink url="http://www.loc.gov/standards/sru/srw/">SRW</ulink>,