From 6d57200f048519e00295b8e7c671909ba54af3b6 Mon Sep 17 00:00:00 2001
From: Andrei Scripniciuc
 <46186670+andrei-scripniciuc@users.noreply.github.com>
Date: Fri, 16 Feb 2024 11:40:47 -0800
Subject: [PATCH 1/2] feat(AIP-203): Clarify that IDENTIFIER fields are
 mutually exclusive with other behaviors

---
 aip/general/0203.md | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/aip/general/0203.md b/aip/general/0203.md
index 7de5e39f2a..1077f335d9 100644
--- a/aip/general/0203.md
+++ b/aip/general/0203.md
@@ -29,7 +29,8 @@ RecognitionAudio audio = 2 [(google.api.field_behavior) = REQUIRED];
 - The annotation **must** include any [google.api.FieldBehavior][] values that
   accurately describe the behavior of the field.
   - `FIELD_BEHAVIOR_UNSPECIFIED` **must not** be used.
-- APIs **must** at minimum use one of `REQUIRED`, `OPTIONAL`, or `OUTPUT_ONLY`.
+- APIs **must** at minimum use one of `REQUIRED`, `OPTIONAL`, `OUTPUT_ONLY` or
+  `IDENTIFIER`.
 
 **Warning:** Although `field_behavior` does not impact proto-level behavior,
 many clients (e.g. CLIs and SDKs) rely on them to generate code. Thoroughly
@@ -78,6 +79,9 @@ resource as the primary input e.g. [Standard Update][aip-134].
 This annotation **must not** be applied to references to other resources within
 a message.
 
+Fields annonated with `IDENTIFIER` **must not** use any other
+`google.api.field_behavior` annotation.
+
 ### Immutable
 
 The use of `IMMUTABLE` indicates that a field on a resource cannot be changed

From a32a82be6f0582ea18ba083830d5e7c88218d3a5 Mon Sep 17 00:00:00 2001
From: Andrei Scripniciuc
 <46186670+andrei-scripniciuc@users.noreply.github.com>
Date: Fri, 16 Feb 2024 19:48:44 +0000
Subject: [PATCH 2/2] chore: add changelog entry

---
 aip/general/0203.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/aip/general/0203.md b/aip/general/0203.md
index 1077f335d9..ec20058e2a 100644
--- a/aip/general/0203.md
+++ b/aip/general/0203.md
@@ -289,6 +289,8 @@ surpass the costs to clients and API users of not doing so.
 
 ## Changelog
 
+- **2024-02-16**: `IDENTIFIER` annotations are mutually exclusive with all
+  other field behaviors. 
 - **2023-09-14**: Clarify that nested behavior and parent behavior are
   independent.
 - **2023-08-25**: Add guidance on `IDENTIFIER`.