message: governance: formalize xDS API shepherds.
  Covers membership criteria, role of xDS API shepherds and what the relationship with UDPA-WG is.
diff: @@ -150,6 +150,37 @@ If a maintainer is no longer interested or cannot perform the maintainer duties
  should volunteer to be moved to emeritus status. In extreme cases this can also occur by a vote of
  the maintainers per the voting process below.
  +# xDS API shepherds
  +
  +The [xDS API shepherds](https://github.com/orgs/envoyproxy/teams/api-shepherds) are responsible for
  +approving any PR that modifies the [api/](api/) tree. They ensure that API [style](api/STYLE.md) and
  +[versioning](api/API_VERSIONING.md) policies are enforced and that a consistent approach is taken
  +towards API evolution.
  +
  +The xDS API shepherds are also the xDS API maintainers; they work collaboratively with the community
  +to drive the xDS API roadmap and review major proposed design changes. The API shepherds are
  +intended to be representative of xDS client and control plane developers who are actively working on
  +xDS development and evolution.
  +
  +As with maintainers, an API shepherd should be spending at least 25% of their time working on xDS
  +developments and expect to be active in this space in the near future. API shepherds are expected to
  +take on API shepherd review load and participate in meetings. They should be active on Slack `#xds`
  +and responsive to GitHub issues and PRs on which they are tagged.
  +
  +The API shepherds are distinct to the [UDPA working
  +group](https://github.com/cncf/udpa/blob/master/README.md), which aims to evolve xDS directionally
  +towards a universal dataplane API. API shepherds are responsible for the execution of the xDS
  +day-to-day and guiding xDS implementation changes. Proposals from UDPA-WG will be aligned with the
  +xDS API shepherds to ensure that xDS is heading towards the UDPA goal. xDS API shepherds operate
  +under the [envoyproxy](https://github.com/envoyproxy) organization but are expected to keep in mind
  +the needs of all xDS clients (currently Envoy and gRPC, but we are aware of other in-house
  +implementations) and the goals of UDPA-WG.
  +
  +If you wish to become an API shepherd and satisfy the above criteria, please contact an existing
  +API shepherd. We will factor in PR and review history to determine if the above API shepherd
  +requirements are met. We may ask you to shadow an existing API shepherd for a period of time to
  +build confidence in consistent application of the API guidelines to PRs.
  +
  # Extension addition policy
  Adding new [extensions](REPO_LAYOUT.md#sourceextensions-layout) has a dedicated policy. Please
  