Further guidance on RFC6570 and delimiters

Also give Appendix C a better name because it is relevant
whether you are using an actual RFC6570 implementation or not.

Author: handrews

versions/3.1.1.md

@@ -1169,12 +1169,12 @@ Serializing with `schema` is NOT RECOMMENDED for `in: "cookie"` parameters, `in:
 | ---- | :----: | ---- |
 | <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 in the query string](https://datatracker.ietf.org/doc/html/rfc3986#section-3.4) (`[`, `]`, `#`), or have a special meaning in `application/x-www-form-urlencoded` (`-`, `&`, `+`); see Appendices [C](#appendix-c-using-rfc6570-implementations) and [E](#appendix-e-percent-encoding-and-form-media-types) for details. This field only applies to parameters with an `in` value of `query`. 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 in the query string](https://datatracker.ietf.org/doc/html/rfc3986#section-3.4) (`[`, `]`, `#`), or have a special meaning in `application/x-www-form-urlencoded` (`-`, `&`, `+`); see Appendices [C](#appendix-c-using-rfc6570-based-serialization) and [E](#appendix-e-percent-encoding-and-form-media-types) for details. This field only applies to parameters with an `in` value of `query`. The default value is `false`. |
 | <a name="parameter-schema"></a>schema | [Schema Object](#schema-object) | The schema defining the type used for the parameter. |
 | <a name="parameter-example"></a>example | Any | Example of the parameter's potential value; see [Working With Examples](#working-with-examples). |
 | <a name="parameter-examples"></a>examples | Map[ `string`, [Example Object](#example-object) \| [Reference Object](#reference-object)] | Examples of the parameter's potential value; see [Working With Examples](#working-with-examples). |
 
-See also [Appendix C: Using RFC6570 Implementations](#appendix-c-using-rfc6570-implementations) for additional guidance.
+See also [Appendix C: Using RFC6570-Based Serialization](#appendix-c-using-rfc6570-based-serialization) for additional guidance.
 
 ###### Fixed Fields for use with `content`
 
@@ -1216,7 +1216,7 @@ The following table shows examples, as would be shown with the `example` or `exa
 * The value _empty_ denotes the empty string, and is unrelated to the `allowEmptyValue` field
 * 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`, each example is shown prefixed with `?` as if it were the only query parameter; see [Appendix C](#appendix-c-using-rfc6570-implementations) 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
+* For `form` and the non-RFC6570 query string styles `spaceDelimited`, `pipeDelimited`, and `deepObject`, each example is shown prefixed with `?` as if it were the only query parameter; 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
 * Note that the `?` prefix is not appropriate for serializing `application/x-www-form-urlencoded` HTTP message bodies, and MUST be stripped or (if constructing the string manually) not added when used in that context; see the [Encoding Object](#encoding-object) for more information
 * 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.
 
@@ -1671,9 +1671,9 @@ 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 request body 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 request body 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 query string](https://datatracker.ietf.org/doc/html/rfc3986#section-3.4) (`[`, `]`, `#`), or have a special meaning in `application/x-www-form-urlencoded` (`-`, `&`, `+`); see Appendices [C](#appendix-c-using-rfc6570-implementations) and [E](#appendix-e-percent-encoding-and-form-media-types) for details. The default value is `false`. This field SHALL be ignored if the request body 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 query string](https://datatracker.ietf.org/doc/html/rfc3986#section-3.4) (`[`, `]`, `#`), or have a special meaning in `application/x-www-form-urlencoded` (`-`, `&`, `+`); 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 request body 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. |
 
-See also [Appendix C: Using RFC6570 Implementations](#appendix-c-using-rfc6570-implementations) for additional guidance, including on difficulties caused by the interaction between RFC6570's percent-encoding rules and the `multipart/form-data` media type.
+See also [Appendix C: Using RFC6570 Implementations](#appendix-c-using-rfc6570-based-serialization) for additional guidance, including on difficulties caused by the interaction between RFC6570's percent-encoding rules and the `multipart/form-data` media type.
 
 Note that the presence of at least one of `style`, `explode`, or `allowReserved` with an explicit value is equivalent to using `schema` with `in: "query"` Parameter Objects.
 The absence of all three of those fields is the equivalent of using `content`, but with the media type specified in `contentType` rather than through a Media Type Object.
@@ -2576,7 +2576,7 @@ The `example` and `examples` fields are mutually exclusive, and if either is pre
 | <a name="header-example"></a>example | Any | Example of the header's potential value; see [Working With Examples](#working-with-examples). |
 | <a name="header-examples"></a>examples | Map[ `string`, [Example Object](#example-object) \| [Reference Object](#reference-object)] | Examples of the header's potential value; see [Working With Examples](#working-with-examples). |
 
-See also [Appendix C: Using RFC6570 Implementations](#appendix-c-using-rfc6570-implementations) for additional guidance.
+See also [Appendix C: Using RFC6570-Based Serialization](#appendix-c-using-rfc6570-based-serialization) for additional guidance.
 
 ###### Fixed Fields for use with `content`
 
@@ -4187,7 +4187,7 @@ However, care must be taken with `format` to ensure that the specific formats ar
 
 Requiring input as pre-formatted, schema-validated strings also improves round-trip interoperability as not all programming languages and environments support the same data types.
 
-## Appendix C: Using RFC6570 Implementations
+## Appendix C: Using RFC6570-Based Serialization
 
 Serialization is defined in terms of [RFC6570](https://www.rfc-editor.org/rfc/rfc6570) URI Templates in two scenarios:
 
@@ -4242,6 +4242,15 @@ The `&` prefix operator has no equivalent in the Parameter Object.
 
 Note that RFC6570 does not specify behavior for compound values beyond the single level addressed by `explode`. The results of using objects or arrays where no behavior is clearly specified for them is implementation-defined.
 
+### Delimiters in Parameter Values
+
+Delimiters used by RFC6570 expansion, such as the `,` used to join arrays or object values with `style: "simple"`, are all automatically percent-encoded as long as `allowReserved` is `false`.
+Note that since RFC6570 does not define a way to parse variables based on a URI Template, users must take care to first split values by delimiter before percent-decoding values that might contain the delimiter character.
+
+When `allowReserved` is `true`, both percent-encoding (prior to joining values with a delimiter) and percent-decoding (after splitting on the delimiter) must be done manually at the correct time.
+
+See [Appendix E](#appendix-e-percent-encoding-and-form-media-types) for additional guidance on handling delimiters for `style` values with no RFC6570 equivalent that already need to be percent-encoded when used as delimiters.
+
 ### Non-RFC6570 Field Values and Combinations
 
 Configurations with no direct [RFC6570](https://datatracker.ietf.org/doc/html/rfc6570) equivalent SHOULD also be handled according to RFC6570.
@@ -4448,7 +4457,7 @@ With `style: "simple"`, that delimiter would itself be percent-encoded, violatin
 Using `style: "form"` with `in: "cookie"` is ambiguous for a single value, and incorrect for multiple values.
 This is true whether the multiple values are the result of using `explode: true` or not.
 
-This style is specified to be equivalent to RFC6570 form expansion which includes the `?` character (see [Appendix C](#appendix-c-using-rfc6570-implementations) for more details), which is not part of the cookie syntax.
+This style is specified to be equivalent to RFC6570 form expansion which includes the `?` character (see [Appendix C](#appendix-c-using-rfc6570-based-serialization) for more details), which is not part of the cookie syntax.
 However, examples of this style in past versions of this specification have not included the `?` prefix, suggesting that the comparison is not exact.
 Because implementations that rely on an RFC6570 implementation and those that perform custom serialization based on the style example will produce different results, it is implementation-defined as to which of the two results is correct.
 
@@ -4475,7 +4484,7 @@ Reserved characters with no special meaning defined within a component can be le
 However, other specifications can define special meanings, requiring percent-encoding for those characters outside of the additional special meanings.
 
 The `form-urlencoded` media type defines special meanings for `=` and `&` as delimiters, and `+` as the replacement for the space character (instead of its percent-encoded form of `%20`).
-This means that while these three characters are reserved-but-allowed in query strings by RFC3986, they must be percent-encoded in `form-urlencoded` query strings except when used for their `form-urlencoded` purposes; see [Appendix C](#appendix-c-using-rfc6570-implementations) for an example of handling `+` in form values.
+This means that while these three characters are reserved-but-allowed in query strings by RFC3986, they must be percent-encoded in `form-urlencoded` query strings except when used for their `form-urlencoded` purposes; see [Appendix C](#appendix-c-using-rfc6570-based-serialization) for an example of handling `+` in form values.
 
 ### Percent-Encoding and `form-data`
 
@@ -4499,7 +4508,7 @@ This specification normatively cites the following relevant standards:
 | [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.
-See [Appendix C](#appendix-c-using-rfc6570-implementations) for more details of RFC6570's two different approaches to percent-encoding, including an example involving `+`.
+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) 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.