The field-name type. Defaults to string, but callers that
pass a string-literal union get that union narrowed through to
FuzzyMatch.field.
Stable identifier for the field (for example 'name' or 'identifier').
Reported back as FuzzyMatch.field so callers know which field
produced the match.
The field's text value to score the query against.
One searchable field extracted from an item: a label identifying the field and the text to match against.