Update examples and appendicies for percent-encoding

handrews · handrews · commit f890a3ec6a08 · 2025-08-13T09:03:58.000-07:00
After adding a new section on percent-encoding guidance, this
updates the examples and other supplemental text to match it.
diff --git a/src/oas.md b/src/oas.md
@@ -1157,7 +1157,7 @@ Serializing with `schema` is NOT RECOMMENDED for `in: "cookie"` parameters; see
 | ---- | :----: | ---- |
 | <a name="parameter-style"></a>style | `string` | Describes how the parameter value will be serialized depending on the type of the parameter value. Default values (based on value of `in`): for `"query"` - `"form"`; for `"path"` - `"simple"`; for `"header"` - `"simple"`; for `"cookie"` - `"form"`. |
 | <a name="parameter-explode"></a>explode | `boolean` | When this is true, parameter values of type `array` or `object` generate separate parameters for each value of the array or key-value pair of the map. For other types of parameters this field has no effect. When [`style`](#parameter-style) is `"form"`, the default value is `true`. For all other styles, the default value is `false`. Note that despite `false` being the default for `deepObject`, the combination of `false` with `deepObject` is undefined. |
-| <a name="parameter-allow-reserved"></a>allowReserved | `boolean` | When this is true, parameter values are serialized using reserved expansion, as defined by [RFC6570](https://datatracker.ietf.org/doc/html/rfc6570#section-3.2.3), which allows [RFC3986's reserved character set](https://datatracker.ietf.org/doc/html/rfc3986#section-2.2), as well as percent-encoded triples, to pass through unchanged, while still percent-encoding all other disallowed characters (including `%` outside of percent-encoded triples). Applications are still responsible for percent-encoding reserved characters that are not allowed by the rules of the `in` destination or media type, or are [not allowed in the path by this specification](#path-templating); see Appendices [C](#appendix-c-using-rfc6570-based-serialization) and [E](#appendix-e-percent-encoding-and-form-media-types) for details. The default value is `false`. |
+| <a name="parameter-allow-reserved"></a>allowReserved | `boolean` | When this is true, parameter values are serialized using reserved expansion, as defined by [RFC6570](https://datatracker.ietf.org/doc/html/rfc6570#section-3.2.3), which allows [RFC3986's reserved character set](https://datatracker.ietf.org/doc/html/rfc3986#section-2.2), as well as percent-encoded triples, to pass through unchanged, while still percent-encoding all other disallowed characters (including `%` outside of percent-encoded triples). Applications are still responsible for percent-encoding reserved characters that are not allowed by the rules of the `in` destination or media type, or are [not allowed in the path by this specification](#path-templating); see [URL Percent-Encoding](#url-percent-encoding) for details. The default value is `false`. |
 | <a name="parameter-schema"></a>schema | [Schema Object](#schema-object) | The schema defining the type used for the parameter. |
 
 See also [Appendix C: Using RFC6570-Based Serialization](#appendix-c-using-rfc6570-based-serialization) for additional guidance.
@@ -1187,7 +1187,7 @@ In order to support common ways of serializing simple parameters, a set of `styl
 | pipeDelimited | `array`, `object` | `query` | Pipe separated array values or object properties and values. This option replaces `collectionFormat` equal to `pipes` from OpenAPI 2.0. |
 | deepObject | `object` | `query` | Allows objects with scalar properties to be represented using form parameters. The representation of array or object properties is not defined. |
 
-#### URL Percent-Encoding
+##### URL Percent-Encoding
 
 All API URLs MUST successfully parse and percent-decode using [[RFC3986]] rules.
 
@@ -1248,7 +1248,7 @@ The following table shows serialized examples, as would be shown with the `seria
 * The behavior of combinations marked _n/a_ is undefined.
 * The `undefined` column replaces the `empty` column in previous versions of this specification in order to better align with [RFC6570](https://www.rfc-editor.org/rfc/rfc6570.html#section-2.3) terminology, which describes certain values including but not limited to `null` as "undefined" values with special handling; notably, the empty string is _not_ undefined.
 * For `form` and the non-RFC6570 query string styles `spaceDelimited`, `pipeDelimited`, and `deepObject`, see [Appendix C](#appendix-c-using-rfc6570-based-serialization) for more information on constructing query strings from multiple parameters, and [Appendix D](#appendix-d-serializing-headers-and-cookies) for warnings regarding `form` and cookie parameters.
-* The examples are percent-encoded as required by RFC6570 and RFC3986; see [Appendix E](#appendix-e-percent-encoding-and-form-media-types) for a thorough discussion of percent-encoding concerns, including why unencoded `|` (`%7C`), `[` (`%5B`), and `]` (`%5D`) seem to work in some environments despite not being compliant.
+* The examples are percent-encoded as explained in the [URL Percent-Encoding](#url-percent-encoding) section above; see [Appendix E](#appendix-e-percent-encoding-and-form-media-types) for a thorough discussion of percent-encoding concerns, including why unencoded `|` (`%7C`), `[` (`%5B`), and `]` (`%5D`) seem to work in some environments despite not being compliant.
 
 | [`style`](#style-values) | `explode` | `undefined` | `string` | `array` | `object` |
 | ---- | ---- | ---- | ---- | ---- | ---- |
@@ -1990,7 +1990,7 @@ See [Appendix B](#appendix-b-data-type-conversion) for a discussion of data type
 | ---- | :----: | ---- |
 | <a name="encoding-style"></a>style | `string` | Describes how a specific property value will be serialized depending on its type. See [Parameter Object](#parameter-object) for details on the [`style`](#parameter-style) field. The behavior follows the same values as `query` parameters, including default values. Note that the initial `?` used in query strings is not used in `application/x-www-form-urlencoded` message bodies, and MUST be removed (if using an RFC6570 implementation) or simply not added (if constructing the string manually). This field SHALL be ignored if the media type is not `application/x-www-form-urlencoded` or `multipart/form-data`. If a value is explicitly defined, then the value of [`contentType`](#encoding-content-type) (implicit or explicit) SHALL be ignored. |
 | <a name="encoding-explode"></a>explode | `boolean` | When this is true, property values of type `array` or `object` generate separate parameters for each value of the array, or key-value-pair of the map. For other types of properties this field has no effect. When [`style`](#encoding-style) is `"form"`, the default value is `true`. For all other styles, the default value is `false`. Note that despite `false` being the default for `deepObject`, the combination of `false` with `deepObject` is undefined. This field SHALL be ignored if the media type is not `application/x-www-form-urlencoded` or `multipart/form-data`. If a value is explicitly defined, then the value of [`contentType`](#encoding-content-type) (implicit or explicit) SHALL be ignored. |
-| <a name="encoding-allow-reserved"></a>allowReserved | `boolean` | When this is true, parameter values are serialized using reserved expansion, as defined by [RFC6570](https://datatracker.ietf.org/doc/html/rfc6570#section-3.2.3), which allows [RFC3986's reserved character set](https://datatracker.ietf.org/doc/html/rfc3986#section-2.2), as well as percent-encoded triples, to pass through unchanged, while still percent-encoding all other disallowed characters (including `%` outside of percent-encoded triples). Applications are still responsible for percent-encoding reserved characters that are not allowed in the target media type; see Appendices [C](#appendix-c-using-rfc6570-based-serialization) and [E](#appendix-e-percent-encoding-and-form-media-types) for details. The default value is `false`. This field SHALL be ignored if the media type is not `application/x-www-form-urlencoded` or `multipart/form-data`. If a value is explicitly defined, then the value of [`contentType`](#encoding-content-type) (implicit or explicit) SHALL be ignored. |
+| <a name="encoding-allow-reserved"></a>allowReserved | `boolean` | When this is true, parameter values are serialized using reserved expansion, as defined by [RFC6570](https://datatracker.ietf.org/doc/html/rfc6570#section-3.2.3), which allows [RFC3986's reserved character set](https://datatracker.ietf.org/doc/html/rfc3986#section-2.2), as well as percent-encoded triples, to pass through unchanged, while still percent-encoding all other disallowed characters (including `%` outside of percent-encoded triples). Applications are still responsible for percent-encoding reserved characters that are not allowed in the target media type; see [URL Percent-Encoding](#url-percent-encoding) for details. The default value is `false`. This field SHALL be ignored if the media type is not `application/x-www-form-urlencoded` or `multipart/form-data`. If a value is explicitly defined, then the value of [`contentType`](#encoding-content-type) (implicit or explicit) SHALL be ignored. |
 
 When using RFC6570-style serialization for `multipart/form-data`, URI percent-encoding MUST NOT be applied, and the value of `allowReserved` has no effect.
 See also [Appendix C: Using RFC6570 Implementations](#appendix-c-using-rfc6570-based-serialization) for additional guidance.
@@ -2041,10 +2041,10 @@ With this example, consider an `id` of `f81d4fae-7dec-11d0-a765-00a0c91e6bf6` an
 }
 ```
 
-Assuming the most compact representation of the JSON value (with unnecessary whitespace removed), we would expect to see the following request body, where space characters have been replaced with `+` and `+`, `"`, `{`, and `}` have been percent-encoded to `%2B`, `%22`, `%7B`, and `%7D`, respectively:
+Assuming the most compact representation of the JSON value (with unnecessary whitespace removed), we would expect to see the following request body, where space characters have been replaced with `+` and `+`, `"`, `:`, `,`, `{`, and `}` have been percent-encoded to `%2B`, `%22`, `%3A`, `%2C`, `%7B`, and `%7D`, respectively:
 
 ```uri
-id=f81d4fae-7dec-11d0-a765-00a0c91e6bf6&address=%7B%22streetAddress%22:%22123+Example+Dr.%22,%22city%22:%22Somewhere%22,%22state%22:%22CA%22,%22zip%22:%2299999%2B1234%22%7D
+id=f81d4fae-7dec-11d0-a765-00a0c91e6bf6&address=%7B%22streetAddress%22%3A%22123+Example+Dr.%22%2C%22city%22%3A%22Somewhere%22%2C%22state%22%3A%22CA%22%2C%22zip%22%3A%2299999%2B1234%22%7D
 ```
 
 Note that the `id` keyword is treated as `text/plain` per the [Encoding Object](#encoding-object)'s default behavior, and is serialized as-is.
@@ -3108,7 +3108,7 @@ X-Rate-Limit-Limit:
     type: integer
 ```
 
-Requiring that a strong `ETag` header (with a value starting with `"` rather than `W/`) is present. Note the use of `content`, because using `schema` and `style` would require the `"` to be percent-encoded as `%22`:
+Requiring that a strong `ETag` header (with a value starting with `"` rather than `W/`) is present.
 
 ```yaml
 ETag:
@@ -5030,8 +5030,10 @@ Since the `.` usage is not automatic, we'll need to construct an appropriate inp
 
 We'll also need to pre-process the values for `formulas` because while `/` and most other reserved characters are allowed in the query string by RFC3986, `[`, `]`, and `#` [are not](https://datatracker.ietf.org/doc/html/rfc3986#appendix-A), and `&`, `=`, and `+` all have [special behavior](https://www.rfc-editor.org/rfc/rfc1866#section-8.2.1) in the `application/x-www-form-urlencoded` format, which is what we are using in the query string.
 
-Setting `allowReserved: true` does _not_ make reserved characters that are not allowed in URIs allowed, it just allows them to be _passed through expansion unchanged._
-Therefore, any tooling still needs to percent-encode those characters because reserved expansion will not do it, but it _will_ leave the percent-encoded triples unchanged.
+Setting `allowReserved: true` does _not_ make reserved characters that are not allowed in URIs allowed, it just allows them to be _passed through expansion unchanged_, for example because some other specification has defined a particular meaning for them.
+
+Therefore, users still need to percent-encode any reserved characters that are _not_ being passed through due to a special meaning because reserved expansion does not know which reserved characters are being used, and which should still be percent-encoded.
+However, reserved expansion, unlike regular expansion,  _will_ leave the pre-percent-encoded triples unchanged.
 See also [Appendix E](#appendix-e-percent-encoding-and-form-media-types) for further guidance on percent-encoding and form media types, including guidance on handling the delimiter characters for `spaceDelimited`, `pipeDelimited`, and `deepObject` in parameter names and values.
 
 So here is our data structure that arranges the names and values to suit the template above, where values for `formulas` have `[]#&=+` pre-percent encoded (although only `+` appears in this example):
@@ -5193,7 +5195,7 @@ The `form-data` media type allows arbitrary text or binary data in its parts, so
 
 URI percent encoding and the `form-urlencoded` media type have complex specification histories spanning multiple revisions and, in some cases, conflicting claims of ownership by different standards bodies.
 Unfortunately, these specifications each define slightly different percent-encoding rules, which need to be taken into account if the URIs or `form-urlencoded` message bodies will be subject to strict validation.
-(Note that many URI parsers do not perform validation by default.)
+(Note that many URI parsers do not perform validation by default, if at all.)
 
 This specification normatively cites the following relevant standards:
 
@@ -5203,13 +5205,11 @@ This specification normatively cites the following relevant standards:
 | [RFC6570](https://www.rfc-editor.org/rfc/rfc6570) | 03/2012 | style-based serialization | [[RFC3986]] | does not use `+` for <code>form&#8209;urlencoded</code> |
 | [RFC1866](https://datatracker.ietf.org/doc/html/rfc1866#section-8.2.1) | 11/1995 | content-based serialization | [[RFC1738]] | obsoleted by [[HTML401]] [Section 17.13.4.1](https://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.1), [[URL]] [Section 5](https://url.spec.whatwg.org/#urlencoded-serializing) |
 
-Style-based serialization is used in the [Parameter Object](#parameter-object) when `schema` is present, and in the [Encoding Object](#encoding-object) when at least one of `style`, `explode`, or `allowReserved` is present.
+Style-based serialization with percent-encoding is used in the [Parameter Object](#parameter-object) when `schema` is present, and in the [Encoding Object](#encoding-object) when at least one of `style`, `explode`, or `allowReserved` is present.
 See [Appendix C](#appendix-c-using-rfc6570-based-serialization) for more details of RFC6570's two different approaches to percent-encoding, including an example involving `+`.
 
 Content-based serialization is defined by the [Media Type Object](#media-type-object), and used with the [Parameter Object](#parameter-object) and [Header Object](#header-object) when the `content` field is present, and with the [Encoding Object](#encoding-object) based on the `contentType` field when the fields `style`, `explode`, and `allowReserved` are absent.
-Each part is encoded based on the media type (e.g. `text/plain` or `application/json`), and must then be percent-encoded for use in a `form-urlencoded` string.
-
-Note that content-based serialization for `form-data` does not expect or require percent-encoding in the data, only in per-part header values.
+Each part is encoded based on the media type (e.g. `text/plain` or `application/json`), and must then be percent-encoded for use in a `form-urlencoded` string unless the media type already incorporates URI percent-encoding.
 
 #### Interoperability with Historical Specifications
 
@@ -5239,9 +5239,11 @@ The `[`, `]`, `|`, and space characters, which are used as delimiters for the `d
 This requires users to pre-encode the character(s) in some other way in parameter names and values to distinguish them from the delimiter usage when using one of these styles.
 
 The space character is always illegal and encoded in some way by all implementations of all versions of the relevant standards.
-While one could use the `form-urlencoded` convention of `+` to distinguish spaces in parameter names and values from `spaceDelimited` delimiters encoded as `%20`, the specifications define the decoding as a single pass, making it impossible to distinguish the different usages in the decoded result.
+While one could use the `form-urlencoded` convention of `+` to distinguish spaces in parameter names and values from `spaceDelimited` delimiters encoded as `%20`, the specifications define the decoding as a single pass, making it impossible to distinguish the different usages in the decoded result unless a non-standard parsing algorithm is used that separates based on one delimiter before decoding the other.
+Any such non-standard parsing approach will not be interoperable across all tools.
 
-Some environments use `[`, `]`, and possibly `|` unencoded in query strings without apparent difficulties, and WHATWG's generic query string rules do not require percent-encoding them.
+Some environments use `[`, `]`, and possibly `|` unencoded in query strings without apparent difficulties.
+WHATWG's generic query string rules do not require percent-encoding them in non-`form-urlencoded` query strings, although it also excludes them from the set of valid URL Unicode code points.
 Code that relies on leaving these delimiters unencoded, while using regular percent-encoding for them within names and values, is not guaranteed to be interoperable across all implementations.
 
 For maximum interoperability, it is RECOMMENDED to either define and document an additional escape convention while percent-encoding the delimiters for these styles, or to avoid these styles entirely.
