Recommend JSON object encoding of an attribute for non-OTLP

CHANGELOG.md

@@ -31,6 +31,9 @@ release.
 
 ### Common
 
+- Add in-development guidance recommending a JSON object as the string
+  representation for an attribute in non-OTLP protocols.
+  ([#5028](https://github.com/open-telemetry/opentelemetry-specification/pull/5028))
 - Define the Core packages term.
   ([#5046](https://github.com/open-telemetry/opentelemetry-specification/pull/5046))
 

specification/common/README.md

@@ -27,6 +27,7 @@ path_base_for_github_subdir:
     + [Arrays](#arrays)
     + [Maps](#maps)
 - [Attribute](#attribute)
+  * [Attribute representation for non-OTLP](#attribute-representation-for-non-otlp)
   * [Attribute Collections](#attribute-collections)
 - [Attribute Limits](#attribute-limits)
   * [Configurable Parameters](#configurable-parameters)
@@ -195,6 +196,34 @@ See [Requirement Level](https://github.com/open-telemetry/semantic-conventions/b
 See [this document](attribute-type-mapping.md) to find out how to map values obtained
 outside OpenTelemetry into OpenTelemetry attribute values.
 
+### Attribute representation for non-OTLP
+
+**Status**: [Development](../document-status.md)
+
+For non-OTLP protocols that need to
+represent a single `Attribute` as a string, the RECOMMENDED form is a
+[JSON object](https://datatracker.ietf.org/doc/html/rfc8259#section-4)
+containing a single name/value pair (member).
+
+The attribute key SHOULD be represented as a JSON object member
+name.
+
+The attribute value SHOULD be represented as a JSON object member value and
+follow the encoding rules defined in
+[AnyValue representation for non-OTLP protocols](#anyvalue-representation-for-non-otlp-protocols),
+as it would be represented as an element in an [array](#arrays) and a value in
+a [map](#maps).
+
+Examples: `{"http.request.method": "GET"}`, `{"retries": 3}`,
+`{"payload": "aGVsbG8gd29ybGQ="}`, `{"session.id": null}`,
+`{"colors": ["red", "blue"]}`, `{"context": {"nested": true}}`
+
+> [!NOTE]
+> This string representation is lossy. Type information is lost as all
+> values are converted to strings, and precision loss may occur for numeric values
+> (particularly for floating point numbers and large integers that exceed the
+> precision capabilities of the receiving system's string-to-number conversion).
+
 ### Attribute Collections
 
 [Resources](../resource/sdk.md),