Comment:

The FHIR API uses underscores for several fields and resources. For example, _history and _search are RESTful resources prefixed with underscores. Similarly, parameters like _format, _count, and _since use underscores.

We cannot find any documentation or guidances as to when underscores are used in a RESTful resource or parameter name.

We suspect that the underscore prefixed parameters are attempting to distinguish from attributes of the Resource. However, explicit documentation regarding the use of underscores in parameters would be appreciated. This would ensure that those making proposals/change to the FHIR REST API follow a consistent naming strategy/pattern.

We are not sure of the underscore usage for the _history and _search resources. They are not FHIR Resources (though they are REST resources) so perhaps that is the intended distinction? Again, having explicit documentation as to the meaning of the underscore will help those making future proposals/changes to the FHIR API to follow a consistent naming strategy/pattern.