'ti' => 'title',
'se' => 'title-series',
'ut' => 'title-uniform',
'an' => 'authority-number',
'an' => 'koha-auth-number',
'koha-auth-number' => 'authority-number',
'at' => 'authtype',
'he' => 'heading',
'rank' => 'relevance',
-