The CARIN BB IG is considering adding an implicit "_include=*" on searches.

Ignoring whether that is a good idea or not, I noticed that the syntax here doesn't match what I would expect.

https://www.hl7.org/fhir/search.html#revinclude says that values for this search parameter should be 2 or 3 parts:

• The name of the source resource from which the join comes
• The name of the search parameter which must be of type reference
• (Optional) A specific of type of target resource (for when the search parameter refers to multiple possible target types)

It goes on to say that include and _revinclude use the wild card "*" for the _search parameter name (which I interpreted to be just the second part).

So, to me, it is fairly clear that:
1. an _include search for an ExplanationOfBenefits and all search parameters it references would look like this:  _include=ExplanationOfBenefit:*

and

2. there is no way to perform a _revinclude in which any resource type referencing the current resource would be included. (i.e. _revinclude=* or _revinclude=:) is not allowed

However, when I pressed this issue at https://chat.fhir.org/#narrow/stream/204607-CARIN-Blue.20Button.20IG/topic/Call.20Recaps/near/201662385 it seems that everyone else has been using `_include=*` and not including the resource type.

Which is it?!