sort-key Sort Key for Index Entry

Provides an alternative version of the index entry for use as a sort key, for example, an ASCII version replacing an accepted character with an unaccented one.
OPTIONAL on elements: <index-entry>, <index-term>
Value Meaning
Text, numbers, or special characters A version of the index entry for sorting.
Restriction @sort-key is an optional attribute; there is no default.
Tagged Sample

Index entry with an alternate ASCII version for a Spanish name

<index-entry sort-key="Cortes, Hernan">
 <term>Cort&eacute;s, Hern&acute;n</term>