jsonschema-validation.xml

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<rfc category="info" docName="draft-wright-json-schema-validation-00" ipr="trust200902">
    <front>
        <title abbrev="JSON Schema Validation">JSON Schema Validation: A Vocabulary for Structural Validation of JSON</title>

        <author fullname="Austin Wright" initials="A" surname="Wright" role="editor">
            <address>
                <email>aaa@bzfx.net</email>
            </address>
        </author>

        <author fullname="Geraint Luff" initials="G" surname="Luff">
            <address>
                <email>luffgd@gmail.com</email>
            </address>
        </author>

        <date year="2016"/>
        <workgroup>Internet Engineering Task Force</workgroup>
        <keyword>JSON</keyword>
        <keyword>Schema</keyword>
        <keyword>validation</keyword>

        <abstract>
            <t>
                JSON Schema (application/schema+json) has several purposes, one of which is JSON instance validation.
                This document specifies a vocabulary for JSON Schema to describe the meaning of JSON documents,
                provide hints for user interfaces working with JSON data,
                and to make assertions about what a valid document must look like.
            </t>
        </abstract>

        <note title="Note to Readers">
            <t>
                The issues list for this draft can be found at <eref target="https://github.com/json-schema-org/json-schema-spec/issues"/>.
            </t>
            <t>
                For additional information, see <eref target="http://json-schema.org/"/>.
            </t>
            <t>
                To provide feedback, use this issue tracker, the communication methods listed on the homepage, or email the document editors.
            </t>
        </note>
    </front>

    <middle>
        <section title="Introduction">
            <t>
                JSON Schema can be used to require that a given JSON document (an instance)
                satisfies a certain number of criteria. These criteria are asserted by using
                keywords described in this specification. In addition, a set of keywords
                is also defined to assist in interactive, user interface instance generation.
            </t>
            <t>
                This specification will use the terminology defined by the
                <xref target="json-schema">JSON Schema core</xref> specification.
            </t>
        </section>

        <section title="Conventions and Terminology">
            <t>
                <!-- The text in this section has been copied from the official boilerplate,
                and should not be modified.-->

                The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
                "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
                interpreted as described in <xref target="RFC2119">RFC 2119</xref>.
            </t>
            <t>
                This specification uses the term "container instance" to refer to both array and
                object instances. It uses the term "children instances" to refer to array elements
                or object member values.
            </t>
            <t>
                This specification uses the term "property set" to refer to the set of an object's
                member names; for instance, the property set of JSON Object { "a": 1, "b": 2 } is
                [ "a", "b" ].
            </t>
            <t>
                Elements in an array value are said to be unique if no two elements of this array
                are <xref target="json-schema">equal</xref>.
            </t>
        </section>

        <section title="Interoperability considerations">

            <section title="Validation of string instances">
                <t>
                    It should be noted that the nul character (\u0000) is valid in a JSON string. An
                    instance to validate may contain a string value with this character, regardless
                    of the ability of the underlying programming language to deal with such data.
                </t>
            </section>

            <section title="Validation of numeric instances">
                <t>
                    The JSON specification allows numbers with arbitrary precision, and JSON Schema does not add any such bounds.
                    This means that numeric instances processed by JSON Schema can be arbitrarily large and/or
                    have an arbitrarily long decimal part, regardless of the ability of the
                    underlying programming language to deal with such data.
                </t>
            </section>

            <section title="Regular expressions">
                <t>
                    Two validation keywords, "pattern" and "patternProperties", use regular
                    expressions to express constraints. These regular expressions SHOULD
                    be valid according to the <xref target="ecma262">ECMA 262</xref> regular
                    expression dialect.
                </t>
                <t>
                    Furthermore, given the high disparity in regular expression constructs support,
                    schema authors SHOULD limit themselves to the following regular expression
                    tokens:

                    <list>
                        <t>individual Unicode characters, as defined by the <xref
                        target="RFC7159">JSON specification</xref>;</t>
                        <t>simple character classes ([abc]), range character classes ([a-z]);</t>
                        <t>complemented character classes ([^abc], [^a-z]);</t>
                        <t>simple quantifiers: "+" (one or more), "*" (zero or more), "?" (zero or
                        one), and their lazy versions ("+?", "*?", "??");</t>
                        <t>range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at least x, at
                        most y, occurrences), {x,} (x occurrences or more), and their lazy
                        versions;</t>
                        <t>the beginning-of-input ("^") and end-of-input ("$") anchors;</t>
                        <t>simple grouping ("(...)") and alternation ("|").</t>
                    </list>
                </t>
                <t>
                    Finally, implementations MUST NOT take regular expressions to be
                    anchored, neither at the beginning nor at the end. This means, for instance,
                    the pattern "es" matches "expression".
                </t>
            </section>

        </section>

        <section title="General validation considerations">

            <section title="Keywords and instance primitive types">
                <t>
                    Most validation keywords only limit the range of values within a certain primitive type.
                    When the primitive type of the instance is not of the type targeted by the keyword, the
                    validation succeeds.
                </t>
                <t>
                    For example, the "maxLength" keyword will only restrict certain strings (that are too long) from being valid.
                    If the instance is a number, boolean, null, array, or object, the keyword passes validation.
                </t>
            </section>

            <section title="Missing keywords">
                <t>
                    Validation keywords that are missing never restrict validation.
                    In some cases, this no-op behavior is identical to a keyword that exists with certain values,
                    and these values are noted where known.
                </t>
            </section>

            <section title="Linearity">
                <!-- I call this "linear" in the same manner e.g. waves are linear, they don't interact with each other -->
                <t>
                    Validation keywords typically operate independent of each other, without affecting each other.
                </t>
                <t>
                    For author convienence, there are some exceptions:
                    <list>
	                     <t>"additionalProperties", whose behavior is defined in terms of "properties" and "patternProperties"; and</t>
                        <t>"additionalItems", whose behavior is defined in terms of "items"</t>
                    </list>
                </t>
            </section>

        </section>

        <section title="Validation keywords">
            <t>
                Validation keywords in a schema impose requirements for successfully validating an instance.
            </t>

            <section title="multipleOf">
                <t>
                    The value of "multipleOf" MUST be a number, strictly greater than 0.
                </t>
                <t>
                    A numeric instance is only valid if division by this keyword's value results in an integer.
                </t>
            </section>

            <section title="maximum">
            <t>
                The value of "maximum" MUST be a number, representing an upper limit for a numeric instance.
            </t>
            <t>
                If the instance is a number, then this keyword validates if "exclusiveMaximum" is true and instance is less than the provided value,
                or else if the instance is less than or exactly equal to the provided value.
            </t>
            </section>

            <section title="exclusiveMaximum">
                <t>
                    The value of "exclusiveMaximum" MUST be a boolean, representing whether the limit in "maximum" is exclusive or not.
                    An undefined value is the same as false.
                </t>
                <t>
                    If "exclusiveMaximum" is true, then a numeric instance SHOULD NOT be equal to the value specified in "maximum".
                    If "exclusiveMaximum" is false (or not specified), then a numeric instance MAY be equal to the value of "maximum".
                </t>
            </section>

            <section title="minimum">
                <t>
                    The value of "minimum" MUST be a number, representing a lower limit for a numeric instance.
                </t>
                <t>
                    If the instance is a number, then this keyword validates if "exclusiveMinimum" is true and instance is greater than the provided value,
                    or else if the instance is greater than or exactly equal to the provided value.
                </t>
            </section>

            <section title="exclusiveMinimum">
                <t>
                    The value of "exclusiveMinimum" MUST be a boolean, representing whether the limit in "minimum" is exclusive or not.
                    An undefined value is the same as false.
                </t>
                <t>
                    If "exclusiveMinimum" is true, then a numeric instance SHOULD NOT be equal to the value specified in "minimum".
                    If "exclusiveMinimum" is false (or not specified), then a numeric instance MAY be equal to the value of "minimum".
                </t>
            </section>

            <section title="maxLength">
                <t>The value of this keyword MUST be a non-negative integer.</t>
                <t>
                    The value of this keyword MUST be an integer. This integer MUST be
                    greater than, or equal to, 0.
                </t>
                <t>
                    A string instance is valid against this keyword if its
                    length is less than, or equal to, the value of this keyword.
                </t>
                <t>
                    The length of a string instance is defined as the number of its
                    characters as defined by <xref target="RFC7159">RFC 7159</xref>.
                </t>
            </section>

            <section title="minLength">
                <t>
                    A string instance is valid against this keyword if its
                    length is greater than, or equal to, the value of this keyword.
                </t>

                <t>
                    The length of a string instance is defined as the number of its
                    characters as defined by <xref target="RFC7159">RFC 7159</xref>.
                </t>
                <t>
                    The value of this keyword MUST be an integer. This integer MUST be
                    greater than, or equal to, 0.
                </t>
                <t>
                    "minLength", if absent, may be considered as being present with integer
                    value 0.
                </t>
            </section>

            <section title="pattern">
                <t>
                    The value of this keyword MUST be a string. This string SHOULD be a
                    valid regular expression, according to the ECMA 262 regular expression
                    dialect.
                </t>
                <t>
                    A string instance is considered valid if the regular
                    expression matches the instance successfully. Recall: regular
                    expressions are not implicitly anchored.
                </t>
            </section>

            <section title="additionalItems and items">
                <t>
                    The value of "additionalItems" MUST be either a boolean or an object. If
                    it is an object, this object MUST be a valid JSON Schema.
                </t>
                <t>
                    The value of "items" MUST be either a schema or array of schemas.
                </t>
                <t>
                    Successful validation of an array instance with regards to these two
                    keywords is determined as follows:

                    <list>
                        <t>if "items" is not present, or its value is an object, validation
                        of the instance always succeeds, regardless of the value of
                        "additionalItems";</t>
                        <t>if the value of "additionalItems" is boolean value true or an
                        object, validation of the instance always succeeds;</t>
                        <t>if the value of "additionalItems" is boolean value false and the
                        value of "items" is an array, the instance is valid if
                        its size is less than, or equal to, the size of "items".</t>
                    </list>
                </t>
                <t>
                    If either keyword is absent, it may be considered present with an empty
                    schema.
                </t>
            </section>

            <section title="maxItems">
                <t>
                    The value of this keyword MUST be an integer. This integer MUST be
                    greater than, or equal to, 0.
                </t>
                <t>
                    An array instance is valid against "maxItems" if its size is
                    less than, or equal to, the value of this keyword.
                </t>
            </section>

            <section title="minItems">
                <t>
                    The value of this keyword MUST be an integer. This integer MUST be
                    greater than, or equal to, 0.
                </t>
                <t>
                    An array instance is valid against "minItems" if its size is
                    greater than, or equal to, the value of this keyword.
                </t>
                <t>
                    If this keyword is not present, it may be considered present with a
                    value of 0.
                </t>
            </section>

            <section title="uniqueItems">
                <t>
                    The value of this keyword MUST be a boolean.
                </t>
                <t>
                    If this keyword has boolean value false, the instance validates
                    successfully. If it has boolean value true, the instance validates
                    successfully if all of its elements are unique.
                </t>
                <t>
                    If not present, this keyword may be considered present with boolean
                    value false.
                </t>
            </section>

            <section title="contains">
                <t>
                    The value of this keyword MUST be an object.  This object MUST be
                    a valid JSON Schema.
                </t>
                <t>
                    An array instance is valid against "contains" if at least one of
                    its elements is valid against the given schema.
                </t>
            </section>

            <section title="maxProperties">
                <t>
                    The value of this keyword MUST be an integer. This integer MUST be
                    greater than, or equal to, 0.
                </t>
                <t>
                    An object instance is valid against "maxProperties" if its
                    number of properties is less than, or equal to, the value of this
                    keyword.
                </t>
            </section>

            <section title="minProperties">
                <t>
                    The value of this keyword MUST be an integer. This integer MUST be
                    greater than, or equal to, 0.
                </t>
                <t>
                    An object instance is valid against "minProperties" if its
                    number of properties is greater than, or equal to, the value of this
                    keyword.
                </t>
                <t>
                    If this keyword is not present, it may be considered present with a
                    value of 0.
                </t>
            </section>

            <section title="required">
                <t>
                    The value of this keyword MUST be an array. This array MUST have at
                    least one element. Elements of this array MUST be strings, and MUST be
                    unique.
                </t>
                <t>
                    An object instance is valid against this keyword if its
                    property set contains all elements in this keyword's array value.
                </t>
            </section>

            <section title="properties">
                <t>
                    The value of "properties" MUST be an object. Each value of this object
                    MUST be an object, and each object MUST be a valid JSON Schema.
                </t>
                <t>
                    If absent, it can be considered the same as an empty object.
                </t>
            </section>

            <section title="patternProperties">
                <t>
                    The value of "patternProperties" MUST be an object. Each property name
                    of this object SHOULD be a valid regular expression, according to the
                    ECMA 262 regular expression dialect. Each property value of this object
                    MUST be an object, and each object MUST be a valid JSON Schema.
                </t>
                <t>
                    If absent, it can be considered the same as an empty object.
                </t>
            </section>

            <section title="additionalProperties">
                <t>
                    The value of "additionalProperties" MUST be a boolean or a schema.
                </t>
                <t>
                    If "additionalProperties" is absent, it may be considered present with
                    an empty schema as a value.
                </t>
                <t>
                    If "additionalProperties" is true, validation always succeeds.
                </t>
                <t>
                    If "additionalProperties" is false, validation succeeds only if the instance
                    is an object and all properties on the instance were covered by "properties"
                    and/or "patternProperties".
                </t>
                <t>
                    If "additionalProperties" is an object, validate the value as a schema to all
                    of the properties that weren't validated by "properties" nor "patternProperties".
                </t>
            </section>

            <section title="dependencies">
                <t>
                    This keyword specifies rules that are evaluated if the instance is an object and
                    contains a certain property.
                </t>
                <t>
                    This keyword's value MUST be an object. Each property specifies a dependency.
                    Each dependency value MUST be an object or an array.
                </t>
                <t>
                    If the dependency value is an object, it MUST be a valid JSON Schema. If the
                    dependency key is a property in the instance, the dependency value must validate
                    against the entire instance.
                </t>
                <t>
                    If the dependency value is an array, it MUST have at least one element, each
                    element MUST be a string, and elements in the array MUST be unique. If the
                    dependency key is a property in the instance, each of the items in the dependency
                    value must be a property that exists in the instance.
                </t>
            </section>

            <section title="enum">
                <t>
                    The value of this keyword MUST be an array. This array SHOULD have at
                    least one element. Elements in the array SHOULD be unique.
                </t>

                <t>
                    Elements in the array MAY be of any type, including null.
                </t>
                <t>
                    An instance validates successfully against this keyword if its value is
                    equal to one of the elements in this keyword's array value.
                </t>
            </section>

            <section title="type">
                <t>
                    The value of this keyword MUST be either a string or an array. If it is
                    an array, elements of the array MUST be strings and MUST be unique.
                </t>
                <t>
                    String values MUST be one of the seven primitive types defined by
                    the core specification.
                </t>
                <t>
                    An instance matches successfully if its primitive type is one of the
                    types defined by keyword. Recall: "number" includes "integer".
                </t>
            </section>

            <section title="allOf">
                <t>
                    This keyword's value MUST be an array. This array MUST have at least one
                    element.
                </t>
                <t>
                    Elements of the array MUST be objects. Each object MUST be a valid JSON
                    Schema.
                </t>
                <t>
                    An instance validates successfully against this keyword if it validates
                    successfully against all schemas defined by this keyword's value.
                </t>
            </section>

            <section title="anyOf">
                    <t>
                    This keyword's value MUST be an array. This array MUST have at least one
                    element.
                </t>
                <t>
                    Elements of the array MUST be objects. Each object MUST be a valid JSON
                    Schema.
                </t>
                <t>
                    An instance validates successfully against this keyword if it validates
                    successfully against at least one schema defined by this keyword's value.
                </t>
            </section>

            <section title="oneOf">
                <t>
                    This keyword's value MUST be an array. This array MUST have at least one
                    element.
                </t>
                <t>
                    Elements of the array MUST be objects. Each object MUST be a valid JSON
                    Schema.
                </t>
                <t>
                    An instance validates successfully against this keyword if it validates
                    successfully against exactly one schema defined by this keyword's value.
                </t>
            </section>

            <section title="not">
                <t>
                    This keyword's value MUST be an object. This object MUST be a valid JSON
                    Schema.
                </t>
                <t>
                    An instance is valid against this keyword if it fails to validate
                    successfully against the schema defined by this keyword.
                </t>
            </section>

            <section title="definitions">
                <t>
                    This keyword's value MUST be an object. Each member value of this object
                    MUST be a valid JSON Schema.
                </t>
                <t>
                    This keyword plays no role in validation per se. Its role is to provide
                    a standardized location for schema authors to inline JSON Schemas into a
                    more general schema.
                </t>

                <t>
                    As an example, here is a schema describing an array of positive
                    integers, where the positive integer constraint is a subschema in
                    "definitions":

                    <figure>
                        <artwork>
<![CDATA[
{
    "type": "array",
    "items": { "$ref": "#/definitions/positiveInteger" },
    "definitions": {
        "positiveInteger": {
            "type": "integer",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    }
}
]]>
                        </artwork>
                    </figure>
                </t>
            </section>
        </section>

        <section title="Metadata keywords">

            <section title='"title" and "description"'>
                <t>
                    The value of both of these keywords MUST be a string.
                </t>
                <t>
                    Both of these keywords can be used to decorate a user interface with
                    information about the data produced by this user interface. A title will
                    preferrably be short, whereas a description will provide explanation about
                    the purpose of the instance described by this schema.
                </t>
                <t>
                    Both of these keywords MAY be used in root schemas, and in any subschemas.
                </t>
            </section>

            <section title='"default"'>
                <t>
                    There are no restrictions placed on the value of this keyword.
                </t>
                <t>
                    This keyword can be used to supply a default JSON value associated with a
                    particular schema. It is RECOMMENDED that a default value be valid against
                    the associated schema.
                </t>
                <t>
                    This keyword MAY be used in root schemas, and in any subschemas.
                </t>
            </section>

        </section>

        <section title='Semantic validation with "format"'>

            <section title="Foreword">
                <t>
                    Structural validation alone may be insufficient to validate that an instance
                    meets all the requirements of an application. The "format" keyword is defined to
                    allow interoperable semantic validation for a fixed subset of values which are
                    accurately described by authoritative resources, be they RFCs or other external
                    specifications.
                </t>

                <t>
                    The value of this keyword is called a format attribute. It MUST be a string. A
                    format attribute can generally only validate a given set of instance types. If
                    the type of the instance to validate is not in this set, validation for this
                    format attribute and instance SHOULD succeed.
                </t>

            </section>

            <section title="Implementation requirements">
                <t>
                    Implementations MAY support the "format" keyword. Should they choose to do so:

                    <list>
                        <t>they SHOULD implement validation for attributes defined below;</t>
                        <t>they SHOULD offer an option to disable validation for this keyword.</t>
                    </list>

                </t>

                <t>
                    Implementations MAY add custom format attributes. Save for agreement between
                    parties, schema authors SHALL NOT expect a peer implementation to support this
                    keyword and/or custom format attributes.
                </t>
            </section>

            <section title="Defined formats">

                <section title="date-time">
                    <t>
                        This attribute applies to string instances.
                    </t>
                    <t>
                        A string instance is valid against this attribute if it is a valid date
                        representation as defined by <xref target="RFC3339">RFC 3339, section
                        5.6</xref>.
                    </t>
                </section>

                <section title="email">
                    <t>
                        This attribute applies to string instances.
                    </t>
                    <t>
                        A string instance is valid against this attribute if it is a valid
                        Internet email address as defined by <xref target="RFC5322">RFC 5322,
                        section 3.4.1</xref>.
                    </t>
                </section>
                <section title="hostname">
                    <section title="Applicability">
                        <t>
                            This attribute applies to string instances.
                        </t>
                    </section>

                    <section title="Validation">
                        <t>
                            A string instance is valid against this attribute if it is a valid
                            representation for an Internet host name, as defined by <xref
                            target="RFC1034">RFC 1034, section 3.1</xref>.
                        </t>
                    </section>
                </section>

                <section title="ipv4">
                    <t>
                        This attribute applies to string instances.
                    </t>
                    <t>
                        A string instance is valid against this attribute if it is a valid
                        representation of an IPv4 address according to the "dotted-quad" ABNF
                        syntax as defined in <xref target="RFC2673">RFC 2673, section
                        3.2</xref>.
                    </t>
                </section>

                <section title="ipv6">
                    <t>
                        This attribute applies to string instances.
                    </t>
                    <t>
                        A string instance is valid against this attribute if it is a valid
                        representation of an IPv6 address as defined in <xref
                        target="RFC2373">RFC 2373, section 2.2</xref>.
                    </t>
                </section>

                <section title="uri">
                    <t>
                        This attribute applies to string instances.
                    </t>
                    <t>
                        A string instance is valid against this attribute if it is a valid URI,
                        according to <xref target="RFC3986"/>.
                    </t>
                </section>

                <section title="uriref">
                    <t>
                        This attribute applies to string instances.
                    </t>
                    <t>
                        A string instance is valid against this attribute if it is a valid URI Reference (either a URI or a relative-reference),
                        according to <xref target="RFC3986"/>.
                    </t>
                </section>

            </section>
        </section>

        <section title="Security considerations">
            <t>
                JSON Schema validation defines a vocabulary for JSON Schema core and conserns all the security considerations listed there.
            </t>
            <t>
                JSON Schema validation allows the use of Regular Expressions, which have numerous different (often incompatible) implementations.
                Some implementations allow the embedding of arbritrary code, which is outside the scope of JSON Schema and MUST NOT be permitted.
                Regular expressions can often also be crafted to be extremely expensive to compute (with so-called "catastrophic backtracking"),
                resulting in a denial-of-service attack.
            </t>
        </section>

        <section title="IANA Considerations">
            <t>
                This specification does not have any influence with regards to IANA.
            </t>

        </section>
    </middle>

    <back>
        <!-- References Section -->
        <references title="Normative References">
            &RFC2119;
            <reference anchor="json-schema">
                <front>
                    <title>JSON Schema: A Media Type for Describing JSON Documents</title>
                    <author/>
                    <date year="2016" month="October"/>
                </front>
                <seriesInfo name="Internet-Draft" value="draft-wright-json-schema-00" />
            </reference>
        </references>

        <references title="Informative References">
            &RFC1034;
            &RFC2373;
            &RFC2673;
            &RFC3339;
            &RFC3986;
            &RFC7159;
            &RFC5322;
            <reference anchor="ecma262"
            target="http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf">
                <front>
                    <title>ECMA 262 specification</title>
                    <author/>
                    <date/>
                </front>
            </reference>
        </references>

        <section title="Acknowledgments">
            <t>
                Thanks to
                Gary Court,
                Francis Galiegue,
                Kris Zyp,
                and Geraint Luff
                for their work on the initial drafts of JSON Schema.
            </t>
            <t>
                Thanks to
                Jason Desrosiers,
                Daniel Perrett,
                Erik Wilde,
                Ben Hutton,
                Evgeny Poberezkin,
                and Henry H. Andrews
                for their submissions and patches to the document.
            </t>
        </section>

        <section title="ChangeLog">
            <t>
                <cref>This section to be removed before leaving Internet-Draft status.</cref>
            </t>
            <t>
                <list style="hanging">
                    <t hangText="draft-wright-json-schema-validation-00">
                        <list style="symbols">
                            <t>Added additional security considerations</t>
                            <t>Removed reference to "latest version" meta-schema, use numbered version instead</t>
                            <t>Rephrased many keyword definitions for brevity</t>
                            <t>Added "uriref" format that also allows relative URI references</t>
                        </list>
                    </t>
                    <t hangText="draft-fge-json-schema-validation-01">
                        <list style="symbols">
                            <t>Initial draft.</t>
                            <t>Salvaged from draft v3.</t>
                            <t>Redefine the "required" keyword.</t>
                            <t>Remove "extends", "disallow"</t>
                            <t>Add "anyOf", "allOf", "oneOf", "not", "definitions", "minProperties",
                            "maxProperties".</t>
                            <t>"dependencies" member values can no longer be single strings; at
                            least one element is required in a property dependency array.</t>
                            <t>Rename "divisibleBy" to "multipleOf".</t>
                            <t>"type" arrays can no longer have schemas; remove "any" as a possible
                            value.</t>
                            <t>Rework the "format" section; make support optional.</t>
                            <t>"format": remove attributes "phone", "style", "color"; rename
                            "ip-address" to "ipv4"; add references for all attributes.</t>
                            <t>Provide algorithms to calculate schema(s) for array/object
                            instances.</t>
                            <t>Add interoperability considerations.</t>
                        </list>
                    </t>
                </list>
            </t>
        </section>
    </back>
</rfc>