In JAVA-3879, we added expressions related to documents. Expressions that refer to fields, like `doc.getInteger("fieldName")`, are some of the most frequently-needed, but are also relatively verbose.

In our documentation, our examples generally extract these into variables, `var fieldName = ...`. This can be further moved into fields on a custom class, which allows for syntax like `doc.fieldName` or `doc.getFieldName()`. This approach runs into problems when the API itself needs to create such objects (for example, in `map(o -> ...)`, o would be a new instance of a particular object), but a POC created during the recent hackathon resolves these issues.

This would be a non-invasive addition to the API that would make it more accessible for users.