AWS SDK for .NET Documentation
SourceField Property
AmazonAmazon.CloudSearch.ModelTextOptionsSourceField Did this page help you?   Yes   No    Tell us about it...
A string that represents the name of an index field. Field names begin with a letter and can contain the following characters: a-z (lowercase), 0-9, and _ (underscore). The name "score" is reserved and cannot be used as a field name. To reference a document's ID, you can use the name _id.

Constraints:

Length
1 - 64
Pattern
[a-z][a-z0-9_]*

Declaration Syntax
C#
public string SourceField { get; set; }

Assembly: AWSSDK (Module: AWSSDK) Version: 1.5.60.0 (1.5.60.0)