Simplify the JSON/YAML stuff

We don't really need the stuff about character encodings, as it
was there because I was confused about something else.

Also minimize the explanation of the change.

Author: handrews

src/oas.md

@@ -175,16 +175,8 @@ Patterned fields MUST have unique names within the containing object.
 
 In order to preserve the ability to round-trip between YAML and JSON formats, YAML version [1.2](https://yaml.org/spec/1.2/spec.html) is RECOMMENDED along with the additional constraints listed in [[!RFC9512]] [Section 3.4](https://www.rfc-editor.org/rfc/rfc9512.html#name-yaml-and-json).
 
-Previous versions of this specification expressed this requirement in terms of [YAML's JSON schema ruleset](https://yaml.org/spec/1.2/spec.html#id2803231), which defines a subset of the YAML syntax and is unrelated to [[JSON-Schema-2020-12|JSON Schema]].
-Despite its name, this ruleset supports features that are not part of JSON, such as distinguishing between integers and floats (see [Data Types](#data-types)) or supporting `!!float .nan` as a value.
-OAD authors SHOULD NOT rely on any YAML features supported by YAML's JSON schema ruleset that are listed as having interoperability challenges in RFC9512.
-
-#### Character Encoding
-
-Note that as stated in [[RFC8259|JSON]] [Section 8.1](https://www.rfc-editor.org/rfc/rfc8259.html#section-8.1), only JSON encoded using UTF-8 is interoperable, which is extended to JSON-compatible YAML in [[!RFC9512]] [Section 3.4](https://www.rfc-editor.org/rfc/rfc9512.html#name-yaml-and-json).
-
-This specification assumes that all OADs are encoded using UTF-8.
-If an implementation chooses to support additional character encodings, the behavior of any feature relying on the assumption of UTF-8 encoding is implementation-defined.
+The recommendation in previous versions of this specification to restrict YAML to its "JSON" [schema ruleset](https://yaml.org/spec/1.2/spec.html#id2803231) allowed for the inclusion of certain values that (despite the name) cannot be represented in JSON.
+OAD authors SHOULD NOT rely on any such JSON-incompatible YAML values.
 
 ### OpenAPI Description Structure