In some situations, especially when working with classes from third-party libraries, you can index values not exposed as objects' properties.

By customizing the `Client` conventions, you can _include_ just about any value indexed by including delegates whose return value is included when indexing. These delegates can use methods, extension methods, and operations on the properties exposed by the indexed object.

Given a `BlogPost` class with a list of tags, you can include the tag count by configuring the `Client` conventions to include an expression that retrieves it.

You can then search and filter for the indexed value:

You also can supply a delegate to set the value when returned in a search result.