Fully define the "merge" operation

[kwatsen]

The "merge" operation is ill-defined.

From https://mailarchive.ietf.org/arch/msg/netconf/ea-jLmqdufvum-TzipioRV7shXA:

Excerpts from RFCs:

Excerpts from RFC 6241:

• merge: The configuration data identified by the element containing this attribute is merged with the configuration at the corresponding level in the configuration datastore identified by the parameter. This is the default behavior.

Excerpts from RFC 8040:

• edit operation: a RESTCONF operation on a data resource using either a POST, PUT, PATCH, or DELETE method. This is not the same as the NETCONF edit operation (i.e., one of the values for the "nc:operation" attribute: "create", "replace", "merge", "delete", or "remove").

• plain patch: a specific media type for use with the PATCH method; see Section 4.6.1. It can be used for simple "merge" edit operations.

• The PATCH method is equivalent to a "merge" edit operation when using a plain patch (see Section 4.6.1); other media types may provide more granular control.

Excerpts from RFC 8072:

• The "merge", "replace", "create", "delete", and "remove" edit operations have exactly the same meanings as those defined for the "operation" attribute described in Section 7.2 of [RFC6241].

• merge merge the edit value with the target data resource; create if it does not already exist

  NOTE: this last sample is the closest to a definition anywhere!

After some discussion, it seems that implementations commonly:

• combine (not replace) leaf-lists and "bits"
• attempt to collate ordered-by user [leaf-]lists
  • i.e., [A, C] + [B, C] = [A, B, C]
  • since both both 'A' and 'B' come before 'C' and since existing elements have precedence order incoming elements.

[avtobiff]

Create separate issues for bits and leaf-lists?

[avtobiff]

File two erratas and hold for document update.