Names must begin with a letter and can contain the following characters: a-z (lowercase), 0-9, and _ (underscore).
The expression to evaluate for sorting while processing a search request. The Expression syntax is based on JavaScript expressions. For more information, see Configuring Expressions in the Amazon CloudSearch Developer Guide.
A named expression that can be evaluated at search time. Can be used to sort the search results, define other expressions, or return computed information in the search results.