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Internet Engineering Task Force (IETF)                   N. Jenkins, Ed.
Request for Comments: 9610                                      Fastmail
Category: Standards Track                                  December 2024
ISSN: 2070-1721

JSON Meta Application Protocol (JMAP) for Contacts

Abstract

This document specifies a data model for synchronising contact data with a server using the JSON Meta Application Protocol (JMAP).

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9610.

Copyright Notice

Copyright © 2024 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
     1.2.  Terminology
     1.3.  Data Model Overview
     1.4.  Addition to the Capabilities Object
       1.4.1.  urn:ietf:params:jmap:contacts
   2.  AddressBooks
     2.1.  AddressBook/get
     2.2.  AddressBook/changes
     2.3.  AddressBook/set
   3.  ContactCards
     3.1.  ContactCard/get
     3.2.  ContactCard/changes
     3.3.  ContactCard/query
       3.3.1.  Filtering
       3.3.2.  Sorting
     3.4.  ContactCard/queryChanges
     3.5.  ContactCard/set
     3.6.  ContactCard/copy
   4.  Examples
     4.1.  Fetching Initial Data
     4.2.  Changing the Default Address Book
   5.  Internationalisation Considerations
   6.  Security Considerations
   7.  IANA Considerations
     7.1.  JMAP Capability Registration for "contacts"
     7.2.  JMAP Data Type Registration for "AddressBook"
     7.3.  JMAP Data Type Registration for "ContactCard"
     7.4.  JMAP Error Codes Registry
       7.4.1.  addressBookHasContents
     7.5.  JSContact Property Registrations
       7.5.1.  id
       7.5.2.  addressBookIds
       7.5.3.  blobId
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Author's Address

1. Introduction

The JSON Meta Application Protocol (JMAP) [RFC8620] is a generic protocol for synchronising data, such as mail, calendars, or contacts, between a client and a server. It is optimised for mobile and web environments and aims to provide a consistent interface to different data types.

This specification defines a data model for synchronising contacts between a client and a server using JMAP.

1.1. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Type signatures, examples, and property descriptions in this document follow the conventions established in Section 1.1 of [RFC8620]. The Id, UnsignedInt, and UTCDate data types defined in Sections 1.2, 1.3, and 1.4 of [RFC8620] are also used in this document.

1.2. Terminology

The same terminology used in the core JMAP specification (see Section 1.6 of [RFC8620]) is also used in this document.

The terms AddressBook and ContactCard (with these specific capitalizations) are used to refer to the data types defined in this document and instances of those data types.

1.3. Data Model Overview

An Account (see Section 1.6.2 of [RFC8620]) with support for the contact data model contains zero or more AddressBook objects, which is a named collection of zero or more ContactCards. A ContactCard is a representation of a person, company, entity, or a group of such entities in JSContact Card format, as defined in Section 2 of [RFC9553]. Each ContactCard belongs to one or more AddressBooks.

In servers with support for JMAP Sharing [RFC9670], users may see and configure sharing of contact data with others. Sharing permissions are managed per AddressBook.

1.4. Addition to the Capabilities Object

The capabilities object is returned as part of the JMAP Session object; see Section 2 of [RFC8620]. This document defines one additional capability URI.

1.4.1. urn:ietf:params:jmap:contacts

This represents support for the AddressBook and ContactCard data types and associated API methods. The value of this property in the JMAP Session "capabilities" property is an empty object.

The value of this property in an account's "accountCapabilities" property is an object that MUST contain the following information on server capabilities and permissions for that account: 

   *maxAddressBooksPerCard*: UnsignedInt|null
      The maximum number of AddressBooks (see Section 2) that can be
      assigned to a single ContactCard object (see Section 3).  This
      MUST be an integer >= 1, or null for no limit (or rather, the
      limit is always the number of AddressBooks in the account).

*mayCreateAddressBook*: Boolean

The user may create an AddressBook in this account if, and only if, this is true.

2. AddressBooks

An AddressBook is a named collection of ContactCards. All ContactCards are associated with one or more AddressBooks.

An *AddressBook* object has the following properties: 

   *id*: Id (immutable; server-set)
      The id of the AddressBook.

*name*: String

The user-visible name of the AddressBook. This MUST NOT be the empty string and MUST NOT be greater than 255 octets in size when encoded as UTF-8. 

   *description*: String|null (default: null)
      An optional long-form description of the AddressBook that provides
      context in shared environments where users need more than just the
      name.
   
   *sortOrder*: UnsignedInt (default: 0)
      Defines the sort order of AddressBooks when presented in the
      client's UI so it is consistent between devices.  The number MUST
      be an integer in the range 0 <= sortOrder < 2^31.

An AddressBook with a lower order is to be displayed before a AddressBook with a higher order in any list of AddressBooks in the client's UI. AddressBooks with equal order should be sorted in alphabetical order by name. The sorting should take into account locale-specific character order convention. 

   *isDefault*: Boolean (server-set)
      This SHOULD be true for exactly one AddressBook in any account and
      MUST NOT be true for more than one AddressBook within an account.
      The default AddressBook should be used by clients whenever they
      need to choose an AddressBook for the user within this account and
      they do not have any other information on which to make a choice.
      For example, if the user creates a new contact card, the client
      may automatically set the card as belonging to the default
      AddressBook from the user's primary account.

*isSubscribed*: Boolean

True if the user has indicated they wish to see this AddressBook in their client. This SHOULD default to false for AddressBooks in shared accounts that the user has access to and true for any new AddressBooks created by the user themself.

If false, the AddressBook and its contents SHOULD only be displayed when the user explicitly requests it. The UI may offer to the user the option of subscribing to it. 

   *shareWith*: Id[AddressBookRights]|null (default: null)
      A map of the Principal id (Section 2 of [RFC9670]) to rights for
      Principals this AddressBook is shared with.  The Principal to
      which this AddressBook belongs MUST NOT be in this set.  This is
      null if the AddressBook is not shared with anyone or if the server
      does not support [RFC9670].  The value may be modified only if the
      user has the "mayShare" right.  The account id for the Principals
      may be found in the urn:ietf:params:jmap:principals:owner
      capability of the Account to which the AddressBook belongs.
   
   *myRights*: AddressBookRights (server-set)
      The set of access rights the user has in relation to this
      AddressBook.

An *AddressBookRights* object has the following properties:

*mayRead*: Boolean

The user may fetch the ContactCards in this AddressBook.

*mayWrite*: Boolean

The user may create, modify, or destroy all ContactCards in this AddressBook, or move them to or from this AddressBook.

*mayShare*: Boolean

The user may modify the "shareWith" property for this AddressBook.

*mayDelete*: Boolean

The user may delete the AddressBook itself.

2.1. AddressBook/get

This is a standard "/get" method as described in Section 5.1 of [RFC8620]. The "ids" argument may be null to fetch all at once.

2.2. AddressBook/changes

This is a standard "/changes" method as described in Section 5.2 of [RFC8620].

2.3. AddressBook/set

This is a standard "/set" method as described in Section 5.3 of [RFC8620], but with the following additional request arguments: 

   *onDestroyRemoveContents*: Boolean (default: false)
      If false, any attempt to destroy an AddressBook that still has a
      ContactCard in it will be rejected with an
      "addressBookHasContents" SetError.  If true, any ContactCard that
      is in the AddressBook will be removed from it, and if such a
      ContactCard does not belong to any other AddressBook, it will be
      destroyed.
   
   *onSuccessSetIsDefault*: Id|null
      If an id is given, and all creates, updates, and destroys (if any)
      succeed without error, the server will try to set this AddressBook
      as the default.  (For references to AddressBook creations, this is
      equivalent to a creation-reference, so the id will be the creation
      id prefixed with a "#".)

If the id is not found or if the change is not permitted by the server for policy reasons, it MUST be ignored and the current default AddressBook (if any) will remain as such. No error is returned to the client in this case.

As per Section 5.3 of [RFC8620], if the default AddressBook is successfully changed, any changed objects MUST be reported in either the "created" or "updated" argument in the response as appropriate, with the server-set value included.

The "shareWith" property may only be set by users that have the "mayShare" right. When modifying the "shareWith" property, the user cannot give a right to a Principal if the Principal did not already have that right and the user making the change also does not have that right. Any attempt to do so MUST be rejected with a "forbidden" SetError.

Users can subscribe or unsubscribe to an AddressBook by setting the "isSubscribed" property. The server MAY forbid users from subscribing to certain AddressBooks even though they have permission to see them, rejecting the update with a "forbidden" SetError.

The following extra SetError type is defined for "destroy": 

   *addressBookHasContents*:  The AddressBook has at least one
      ContactCard assigned to it and the "onDestroyRemoveContents"
      argument was false.

3. ContactCards

A *ContactCard* object contains information about a person, company, or other entity, or represents a group of such entities. It is a JSContact Card object as defined in Section 2 of [RFC9553] with the following additional properties: 

   *id*: Id (immutable; server-set)
      The id of the ContactCard.  The "id" property MAY be different to
      the ContactCard's "uid" property (as defined in Section 2.1.9 of
      [RFC9553]).  However, there MUST NOT be more than one ContactCard
      with the same uid in an Account.
   
   *addressBookIds*: Id[Boolean]
      The set of AddressBook ids that this ContactCard belongs to.  A
      card MUST belong to at least one AddressBook at all times (until
      it is destroyed).  The set is represented as an object, with each
      key being an AddressBook id.  The value for each key in the object
      MUST be true.

For any Media object in the card (see Section 2.6.4 of [RFC9553]), a new property is defined:

*blobId*: Id

An id for the Blob representing the binary contents of the resource.

When returning ContactCards, any Media with a URI that uses the "data:" URL scheme [RFC2397] SHOULD return a "blobId" property and omit the "uri" property, as this lets clients load the (potentially large) image file only when needed and avoids the overhead of Base64 encoding. The "mediaType" property MUST also be set. Similarly, when creating or updating a ContactCard, clients MAY send a "blobId" instead of the "uri" property for a Media object.

A contact card with a "kind" property equal to "group" represents a group of contacts. Clients often present these separately from other contact cards. The "members" property, as defined in Section 2.1.6 of [RFC9553], contains a set of uids (as defined in Section 2.1.9 of [RFC9553]) for other contacts that are the members of this group. Clients should consider the group to contain any ContactCard with a matching uid from any account they have access to that has support for the urn:ietf:params:jmap:contacts capability. Any uid that cannot be found SHOULD be ignored but preserved. For example, suppose a user adds contacts from a shared address book to their private group, then temporarily loses access to this address book. The uids cannot be resolved, so the contacts will disappear from the group. However, if they are given permission to access the data again, the uids will be found and the contacts will reappear.

3.1. ContactCard/get

This is a standard "/get" method as described in Section 5.1 of [RFC8620].

3.2. ContactCard/changes

This is a standard "/changes" method as described in Section 5.2 of [RFC8620].

3.3. ContactCard/query

This is a standard "/query" method as described in Section 5.5 of [RFC8620].

3.3.1. Filtering

A *FilterCondition* object has the following properties, any of which may be omitted:

*inAddressBook*: Id

An AddressBook id. A card must be in this address book to match the condition.

*uid*: String

A card must have this string exactly as its uid (as defined in Section 2.1.9 of [RFC9553]) to match.

*hasMember*: String

A card must have a "members" property (as defined in Section 2.1.6 of [RFC9553]) that contains this string as one of the uids in the set to match.

*kind*: String

A card must have a "kind" property (as defined in Section 2.1.4 of [RFC9553]) that equals this string exactly to match.

*createdBefore*: UTCDate

The "created" date-time of the ContactCard (as defined in Section 2.1.3 of [RFC9553]) must be before this date-time to match the condition.

*createdAfter*: UTCDate

The "created" date-time of the ContactCard (as defined in Section 2.1.3 of [RFC9553]) must be the same or after this date- time to match the condition.

*updatedBefore*: UTCDate

The "updated" date-time of the ContactCard (as defined in Section 2.1.10 of [RFC9553]) must be before this date-time to match the condition.

*updatedAfter*: UTCDate

The "updated" date-time of the ContactCard (as defined in Section 2.1.10 of [RFC9553]) must be the same or after this date- time to match the condition.

*text*: String

A card matches this condition if the text matches with text in the card.

*name*: String

A card matches this condition if the value of any NameComponent in the "name" property or the "full" property in the "name" property of the card (as defined in Section 2.2.1.2 of [RFC9553]) matches the value. 

   *name/given*: String
      A card matches this condition if the value of a NameComponent with
      kind "given" inside the "name" property of the card (as defined in
      Section 2.2.1.2 of [RFC9553]) matches the value.
   
   *name/surname*: String
      A card matches this condition if the value of a NameComponent with
      kind "surname" inside the "name" property of the card (as defined
      in Section 2.2.1.2 of [RFC9553]) matches the value.
   
   *name/surname2*: String
      A card matches this condition if the value of a NameComponent with
      kind "surname2" inside the "name" property of the card (as defined
      in Section 2.2.1.2 of [RFC9553]) matches the value.

*nickname*: String

A card matches this condition if the "name" of any Nickname in the "nicknames" property of the card (as defined in Section 2.2.2 of [RFC9553]) matches the value.

*organization*: String

A card matches this condition if the "name" of any Organization in the "organizations" property of the card (as defined in Section 2.2.3 of [RFC9553]) matches the value.

*email*: String

A card matches this condition if the "address" or "label" of any EmailAddress in the "emails" property of the card (as defined in Section 2.3.1 of [RFC9553]) matches the value.

*phone*: String

A card matches this condition if the "number" or "label" of any Phone in the "phones" property of the card (as defined in Section 2.3.3 of [RFC9553]) matches the value.

*onlineService*: String

A card matches this condition if the "service", "uri", "user", or "label" of any OnlineService in the "onlineServices" property of the card (as defined in Section 2.3.2 of [RFC9553]) matches the value.

*address*: String

A card matches this condition if the value of any AddressComponent in the "addresses" property or the "full" property in the "addresses" property of the card (as defined in Section 2.5.1 of [RFC9553]) matches the value.

*note*: String

A card matches this condition if the "note" of any Note in the "notes" property of the card (as defined in Section 2.8.3 of [RFC9553]) matches the value.

If zero properties are specified on the FilterCondition, the condition MUST always evaluate to true. If multiple properties are specified, ALL must apply for the condition to be true (it is equivalent to splitting the object into one-property conditions and making them all the child of an AND filter operator).

The exact semantics for matching String fields is deliberately not defined to allow for flexibility in indexing implementation, subject to the following:

  • Text SHOULD be matched in a case-insensitive manner.
  • Text contained in either (but matched) single or double quotes SHOULD be treated as a phrase search. That is, a match is required for that exact sequence of words, excluding the surrounding quotation marks. Use \", \', and \\ to match a literal ", ', and \ respectively in a phrase.
  • Outside of a phrase, whitespace SHOULD be treated as dividing separate tokens that may be searched for separately in the contact, but MUST all be present for the contact to match the filter.
  • Tokens MAY be matched on a whole-word basis using stemming (e.g., a text search for bus would match "buses", but not "business").

3.3.2. Sorting

The following values for the "property" field on the Comparator object MUST be supported for sorting:

  • "created" - The "created" date on the ContactCard.
  • "updated" - The "updated" date on the ContactCard.

The following values for the "property" field on the Comparator object SHOULD be supported for sorting:

  • "name/given" - The value of the first NameComponent in the "name" property whose "kind" is "given".
  • "name/surname" - The value of the first NameComponent in the "name" property whose "kind" is "surname".
  • "name/surname2" - The value of the first NameComponent in the "name" property whose "kind" is "surname2".

3.4. ContactCard/queryChanges

This is a standard "/queryChanges" method as described in Section 5.6 of [RFC8620].

3.5. ContactCard/set

This is a standard "/set" method as described in Section 5.3 of [RFC8620].

To set a new photo, the file must first be uploaded using the upload mechanism as described in Section 6.1 of [RFC8620]. This will give the client a valid blobId, size, and type to use. The server MUST reject attempts to set a file that is not a recognised image type as the photo for a card.

3.6. ContactCard/copy

This is a standard "/copy" method as described in Section 5.4 of [RFC8620].

4. Examples

For brevity, only the "methodCalls" property of the Request object and the "methodResponses" property of the Response object is shown in the following examples.

4.1. Fetching Initial Data

A user has authenticated and the client has fetched the JMAP Session object. It finds a single Account with the "urn:ietf:params:jmap:contacts" capability with id "a0x9" and wants to fetch all the address books and contacts. It might make the following request: 

   [
     ["AddressBook/get", {
       "accountId": "a0x9"
     }, "0"],
     ["ContactCard/get", {
       "accountId": "a0x9"
     }, "1"]
   ]

Figure 1: "methodCalls" Property of a JMAP Request

The server might respond with something like: 

   [
     ["AddressBook/get", {
       "accountId": "a0x9",
       "list": [{
         "id": "062adcfa-105d-455c-bc60-6db68b69c3f3",
         "name": "Personal",
         "description": null,
         "sortOrder": 0,
         "isDefault": true,
         "isSubscribed": true,
         "shareWith": {
           "3f1502e0-63fe-4335-9ff3-e739c188f5dd": {
             "mayRead": true,
             "mayWrite": false,
             "mayShare": false,
             "mayDelete": false
           }
         },
         "myRights": {
           "mayRead": true,
           "mayWrite": true,
           "mayShare": true,
           "mayDelete": false
         }
       }, {
         "id": "cd40089d-35f9-4fd7-980b-ba3a9f1d74fe",
         "name": "Autosaved",
         "description": null,
         "sortOrder": 1,
         "isDefault": false,
         "isSubscribed": true,
         "shareWith": null,
         "myRights": {
           "mayRead": true,
           "mayWrite": true,
           "mayShare": true,
           "mayDelete": false
         }
       }],
       "notFound": [],
       "state": "~4144"
     }, "0"],
     ["ContactCard/get", {
       "accountId": "a0x9",
       "list": [{
         "id": "3",
         "addressBookIds": {
           "062adcfa-105d-455c-bc60-6db68b69c3f3": true
         },
         "name": {
           "components": [
             { "kind": "given", "value": "Joe" },
             { "kind": "surname", "value": "Bloggs" }
           ],
           "isOrdered": true
         },
         "emails": {
           "0": {
             "contexts": {
               "private": true
             },
             "address": "joe.bloggs@example.com"
           }
         }
       }],
       "notFound": [],
       "state": "ewarbckaqJ::112"
     }, "1"]
   ]

Figure 2: "methodResponses" Property of a JMAP Response

4.2. Changing the Default Address Book

The client tries to change the default address book from "Personal" to "Autosaved" (and makes no other change): 

   [
     ["AddressBook/set", {
       "accountId": "a0x9",
       "onSuccessSetIsDefault": "cd40089d-35f9-4fd7-980b-ba3a9f1d74fe"
     }, "0"]
   ]

Figure 3: "methodCalls" Property of a JMAP Request

The server allows the change, returning the following response: 

   [
     ["AddressBook/set", {
       "accountId": "a0x9",
       "updated": {
         "cd40089d-35f9-4fd7-980b-ba3a9f1d74fe": {
           "isDefault": true
         },
         "062adcfa-105d-455c-bc60-6db68b69c3f3": {
           "isDefault": false
         },
         "oldState": "~4144",
         "newState": "~4148"
       }
     }, "0"]
   ]

Figure 4: "methodResponses" Property of a JMAP Response

5. Internationalisation Considerations

Experience has shown that unrestricted use of Unicode can lead to problems such as inconsistent rendering, users reading text and interpreting it differently than intended, and unexpected results when copying text from one location to another. Servers MAY choose to mitigate this by restricting the set of characters allowed in otherwise unconstrained String fields. The FreeformClass, as documented in Section 4.3 of [RFC8264], might be a good starting point for this.

Attempts to set a value containing code points outside of the permissible set can be handled in a few ways by the server. The server could choose to strip the forbidden characters or replace them with U+FFFD (the Unicode replacement character) and store the resulting string. This is likely to be appropriate for non-printable characters -- such as the "Control Codes" defined in Section 23.1 (https://www.unicode.org/versions/latest/core-spec/chapter- 23/#G20365) of [UNICODE], excluding newline (U+000A), carriage return (U+000D), and tab (U+0009) -- that can end up in data accidentally due to copy-and-paste issues but are invisible to the end user. JMAP allows the server to transform data on create/update as long as any changed properties are returned to the client in the "/set" response so it knows what has changed, as per Section 5.3 of [RFC8620]. Alternatively, the server MAY just reject the create/update with an "invalidProperties" SetError.

6. Security Considerations

All security considerations of JMAP [RFC8620] apply to this specification. Additional considerations specific to the data types and functionality introduced by this document are described in the following subsection.

Contacts consist almost entirely of private, personally identifiable information, and represent the social connections of users. Privacy leaks can have real world consequences, and contact servers and clients MUST be mindful of the need to keep all data secure.

Servers MUST enforce the Access Control Lists (ACLs) set on address books to ensure only authorised data is shared.

7. IANA Considerations

7.1. JMAP Capability Registration for "contacts"

IANA has registered "contacts" in the "JMAP Capabilities" registry as follows: 

   Capability Name:  urn:ietf:params:jmap:contacts
   Intended Use:  common
   Change Controller:  IETF
   Security and Privacy Considerations:  this document, Section 6
   Reference:  this document

7.2. JMAP Data Type Registration for "AddressBook"

IANA has registered "AddressBook" in the "JMAP Data Types" registry as follows: 

   Type Name:  AddressBook
   Can Reference Blobs:  No
   Can Use for State Change:  Yes
   Capability:  urn:ietf:params:jmap:contacts
   Reference:  this document

7.3. JMAP Data Type Registration for "ContactCard"

IANA has registered "ContactCard" in the "JMAP Data Types" registry as follows: 

   Type Name:  ContactCard
   Can Reference Blobs:  Yes
   Can Use for State Change:  Yes
   Capability:  urn:ietf:params:jmap:contacts
   Reference:  this document

7.4. JMAP Error Codes Registry

The following subsection has registered a new error code in the "JMAP Error Codes" registry, as defined in Section 9 of [RFC8620].

7.4.1. addressBookHasContents

   JMAP Error Code:  addressBookHasContents
   Intended Use:  common
   Change Controller:  IETF
   Description:  The AddressBook has at least one ContactCard assigned
      to it, and the "onDestroyRemoveContents" argument was false.
   Reference:  This document, Section 2.3

7.5. JSContact Property Registrations

IANA has registered the following additional properties in the "JSContact Properties" registry, as defined in Section 3 of [RFC9553].

7.5.1. id

   Property Name:  id
   Property Type:  not applicable
   Property Context:  Card
   Intended Usage:  reserved
   Since Version:  1.0
   Change Controller:  IETF
   Reference:  this document

7.5.2. addressBookIds

   Property Name:  addressBookIds
   Property Type:  not applicable
   Property Context:  Card
   Intended Usage:  reserved
   Since Version:  1.0
   Change Controller:  IETF
   Reference:  this document

7.5.3. blobId

   Property Name:  blobId
   Property Type:  not applicable
   Property Context:  Media
   Intended Usage:  reserved
   Since Version:  1.0
   Change Controller:  IETF
   Reference:  this document

8. References

8.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.
   
   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397,
              DOI 10.17487/RFC2397, August 1998,
              <https://www.rfc-editor.org/info/rfc2397>.
   
   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.
   
   [RFC8620]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July
              2019, <https://www.rfc-editor.org/info/rfc8620>.
   
   [RFC9553]  Stepanek, R. and M. Loffredo, "JSContact: A JSON
              Representation of Contact Data", RFC 9553,
              DOI 10.17487/RFC9553, May 2024,
              <https://www.rfc-editor.org/info/rfc9553>.
   
   [RFC9670]  Jenkins, N., Ed., "JSON Meta Application Protocol (JMAP)
              Sharing", RFC 9670, DOI 10.17487/RFC9670, November 2024,
              <https://www.rfc-editor.org/info/rfc9670>.

8.2. Informative References

   [RFC8264]  Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
              Preparation, Enforcement, and Comparison of
              Internationalized Strings in Application Protocols",
              RFC 8264, DOI 10.17487/RFC8264, October 2017,
              <https://www.rfc-editor.org/info/rfc8264>.
   
   [UNICODE]  The Unicode Consortium, "The Unicode Standard",
              <https://www.unicode.org/versions/latest/>.

Author's Address

   Neil Jenkins (editor)
   Fastmail
   PO Box 234, Collins St West
   Melbourne  VIC 8007
   Australia
   Email: neilj@fastmailteam.com
   URI:   https://www.fastmail.com