draft-ietf-appsawg-json-patch-05.txt   draft-ietf-appsawg-json-patch-06.txt 
Applications Area Working Group P. Bryan, Ed. Applications Area Working Group P. Bryan, Ed.
Internet-Draft Salesforce.com Internet-Draft Salesforce.com
Intended status: Informational M. Nottingham, Ed. Intended status: Informational M. Nottingham, Ed.
Expires: March 30, 2013 September 26, 2012 Expires: April 25, 2013 October 22, 2012
JSON Patch JSON Patch
draft-ietf-appsawg-json-patch-05 draft-ietf-appsawg-json-patch-06
Abstract Abstract
JSON Patch defines the media type "application/json-patch", a JSON JSON Patch defines the media type "application/json-patch", a JSON
document structure for expressing a sequence of operations to apply document structure for expressing a sequence of operations to apply
to a JSON document. to a JSON document.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 30, 2013. This Internet-Draft will expire on April 25, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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4.1. add . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. add . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. remove . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. remove . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. replace . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.3. replace . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. move . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.4. move . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.5. copy . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.5. copy . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.6. test . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.6. test . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 10
A.1. Adding an Object Member . . . . . . . . . . . . . . . . . 10 A.1. Adding an Object Member . . . . . . . . . . . . . . . . . 10
A.2. Adding an Array Element . . . . . . . . . . . . . . . . . 11 A.2. Adding an Array Element . . . . . . . . . . . . . . . . . 11
A.3. Removing an Object Member . . . . . . . . . . . . . . . . 11 A.3. Removing an Object Member . . . . . . . . . . . . . . . . 11
A.4. Removing an Array Element . . . . . . . . . . . . . . . . 11 A.4. Removing an Array Element . . . . . . . . . . . . . . . . 11
A.5. Replacing a Value . . . . . . . . . . . . . . . . . . . . 12 A.5. Replacing a Value . . . . . . . . . . . . . . . . . . . . 12
A.6. Moving a Value . . . . . . . . . . . . . . . . . . . . . . 12 A.6. Moving a Value . . . . . . . . . . . . . . . . . . . . . . 12
A.7. Moving an Array Element . . . . . . . . . . . . . . . . . 13 A.7. Moving an Array Element . . . . . . . . . . . . . . . . . 13
A.8. Testing a Value: Success . . . . . . . . . . . . . . . . . 13 A.8. Testing a Value: Success . . . . . . . . . . . . . . . . . 14
A.9. Testing a Value: Error . . . . . . . . . . . . . . . . . . 14 A.9. Testing a Value: Error . . . . . . . . . . . . . . . . . . 14
A.10. Adding a nested Member Object . . . . . . . . . . . . . . 14 A.10. Adding a nested Member Object . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 A.11. Ignoring Unrecognized Elements . . . . . . . . . . . . . . 15
A.12. Adding to a Non-existant Target . . . . . . . . . . . . . 15
A.13. Invalid JSON Patch Document . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
JavaScript Object Notation (JSON) [RFC4627] is a common format for JavaScript Object Notation (JSON) [RFC4627] is a common format for
the exchange and storage of structured data. HTTP PATCH [RFC5789] the exchange and storage of structured data. HTTP PATCH [RFC5789]
extends the Hypertext Transfer Protocol (HTTP) [RFC2616] with a extends the Hypertext Transfer Protocol (HTTP) [RFC2616] with a
method to perform partial modifications to resources. method to perform partial modifications to resources.
JSON Patch is a format (identified by the media type "application/ JSON Patch is a format (identified by the media type "application/
json-patch") for expressing a sequence of operations to apply to a json-patch") for expressing a sequence of operations to apply to a
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2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
See Section 5 for information about handling errors. See Section 5 for information about handling errors.
3. Document Structure 3. Document Structure
A JSON Patch document is a JSON [RFC4627] document whose root object A JSON Patch document is a JSON [RFC4627] document whose root is an
is an array of objects. Each object represents a single operation to array of objects. Each object represents a single operation to be
be applied to the target JSON document. applied to the target JSON document.
An example JSON Patch document: An example JSON Patch document:
[ [
{ "op": "test", "path": "/a/b/c", "value": "foo" }, { "op": "test", "path": "/a/b/c", "value": "foo" },
{ "op": "remove", "path": "/a/b/c" }, { "op": "remove", "path": "/a/b/c" },
{ "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] }, { "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] },
{ "op": "replace", "path": "/a/b/c", "value": 42 }, { "op": "replace", "path": "/a/b/c", "value": 42 },
{ "op": "move", "path": "/a/b/c", "to": "/a/b/d" }, { "op": "move", "path": "/a/b/c", "to": "/a/b/d" },
{ "op": "copy", "path": "/a/b/c", "to": "/a/b/e" } { "op": "copy", "path": "/a/b/d", "to": "/a/b/e" }
] ]
Evaluation of a JSON Patch document begins with a target JSON Evaluation of a JSON Patch document begins with a target JSON
document. Operations are applied sequentially in the order they document. Operations are applied sequentially in the order they
appear in the array. Each operation in the sequence is applied to appear in the array. Each operation in the sequence is applied to
the target document; the resulting document becomes the target of the the target document; the resulting document becomes the target of the
next operation. Evaluation continues until all operations are next operation. Evaluation continues until all operations are
successfully applied, or an error condition is encountered. successfully applied, or an error condition is encountered.
4. Operations 4. Operations
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o the root of the target document, o the root of the target document,
o a member to add to an existing object, or o a member to add to an existing object, or
o an element to add to an existing array. o an element to add to an existing array.
For example: For example:
{ "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] } { "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] }
If the target location references the root of the target document or
a member of an existing object, the specified location MUST already
exist for the operation to be successful.
If the target location references an element of an existing array, If the target location references an element of an existing array,
any elements at or above the specified index are shifted one position any elements at or above the specified index are shifted one position
to the right. The specified index MUST NOT be greater than the to the right. The specified index MUST NOT be greater than the
number of elements in the array. number of elements in the array.
When the "-" character is used to index the end of the array, this
has the effect of appending the value to the array.
Note that this operation will, in common use, have a target location Note that this operation will, in common use, have a target location
that does not resolve to an existing value, resulting in the that does not resolve to an existing value, resulting in the
pointer's error handling algorithm being invoked. This specification pointer's error handling algorithm being invoked. This specification
defines the error handling algorithm for "add" pointers to explicitly defines the error handling algorithm for "add" pointers to explicitly
ignore the error and perform the operation as specified. ignore the error and perform the operation as specified.
4.2. remove 4.2. remove
The "remove" operation removes the value at the specified location. The "remove" operation removes the value at the target location.
The value at the specified location MUST exist for the operation to The target location MUST exist for the operation to be successful.
be successful.
For example: For example:
{ "op": "remove", "path": "/a/b/c" } { "op": "remove", "path": "/a/b/c" }
If removing an element from an array, any elements above the If removing an element from an array, any elements above the
specified index are shifted one position to the left. specified index are shifted one position to the left.
4.3. replace 4.3. replace
The "replace" operation replaces the value at the specified location The "replace" operation replaces the value at the target location
with a new value. The operation object MUST contain a "value" member with a new value. The operation object MUST contain a "value" member
that specifies the replacement value. that specifies the replacement value.
The value at the specified location MUST exist for the operation to The target location MUST exist for the operation to be successful.
be successful.
For example: For example:
{ "op": "replace", "path": "/a/b/c", "value": 42 } { "op": "replace", "path": "/a/b/c", "value": 42 }
This operation is functionally identical to expressing a "remove" This operation is functionally identical to expressing a "remove"
operation for a value, followed immediately by an "add" operation at operation for a value, followed immediately by an "add" operation at
the same location with the replacement value. the same location with the replacement value.
4.4. move 4.4. move
The "move" operation removes the value at the specified location and The "move" operation removes the value at the target location and
adds it to another location in the target document. adds it to another location.
The operation object MUST contain a "to" member, a string containing The operation object MUST contain a "to" member, a string containing
a JSON Pointer value that references the location in the target a JSON Pointer value that references the location in the target
document to add the value to. document to add the value to.
The "to" location MUST reference one of: The "to" location MUST reference one of:
o the member to add to an existing object, or o the member to add to an existing object, or
o an element to add to an existing array. o an element to add to an existing array.
For example: For example:
{ "op": "move", "path": "/a/b/c", "to": "/a/b/d" } { "op": "move", "path": "/a/b/c", "to": "/a/b/d" }
This operation is functionally identical to expressing a "remove" This operation is functionally identical to expressing a "remove"
operation on the specified location, followed immediately by an "add" operation on the target location, followed immediately by an "add"
operation at the "to" location with the value that was just removed. operation at the "to" location with the value that was just removed.
The location in the "to" member MUST NOT be part of the location
defined by "path"; i.e., a location cannot be moved into one of its
children.
The location in the "to" member MUST NOT reference a member of an The location in the "to" member MUST NOT reference a member of an
existing object in the target document, unless "move" and "to" existing object in the target document, unless "path" and "to"
specify the same object, which has no effect. specify the same object, which has no effect.
If the location in the "to" member references an element of an If the location in the "to" member references an element of an
existing array, any elements at or above the specified index are existing array, any elements at or above the specified index are
shifted one position to the right. The specified index MUST NOT be shifted one position to the right. The specified index MUST NOT be
greater than the number of elements in the array. greater than the number of elements in the array.
4.5. copy 4.5. copy
The "copy" operation copies the value at the specified location to The "copy" operation copies the value at the target location to
another location in the target document. another location.
The operation object MUST contain a "to" member, a string containing The operation object MUST contain a "to" member, a string containing
a JSON Pointer value that references the location in the target a JSON Pointer value that references the location in the target
document to add the value to. document to add the value to.
This location MUST reference one of: This location MUST reference one of:
o the member to add to an existing object, or o the member to add to an existing object, or
o an element to add to an existing array. o an element to add to an existing array.
For example: For example:
{ "op": "copy", "path": "/a/b/c", "to": "/a/b/e" } { "op": "copy", "path": "/a/b/c", "to": "/a/b/e" }
The location in the "to" member MUST NOT be part of the location
defined by "path"; i.e., a location cannot be copied into one of its
children.
The location in the "to" member MUST NOT reference a member of an The location in the "to" member MUST NOT reference a member of an
existing object in the target document, unless "move" and "to" existing object in the target document, unless "path" and "to"
specify the same object, which has no effect. specify the same object, which has no effect.
If the location in the "to" member references an element of an If the location in the "to" member references an element of an
existing array, any elements at or above the specified index are existing array, any elements at or above the specified index are
shifted one position to the right. The specified index MUST NOT be shifted one position to the right. The specified index MUST NOT be
greater than the number of elements in the array. greater than the number of elements in the array.
4.6. test 4.6. test
The "test" operation tests that a value at the specified location is The "test" operation tests that a value at the target location is
equal to a value. equal to a specified value.
The operation object MUST contain a "value" member that conveys the The operation object MUST contain a "value" member that conveys the
value to be compared to that at the specified location. value to be compared to that at the target location.
The value at the specified location MUST be equal to the specified The target location MUST be equal to the "value" value for the
value for the operation to be considered successful. operation to be considered successful.
Here, "equal" means that the value at the specified location and the Here, "equal" means that the value at the target location and the
value conveyed by "value" are of the same JSON type, and considered value conveyed by "value" are of the same JSON type, and considered
equal by the following rules for that type: equal by the following rules for that type:
o strings: are considered equal if, after unescaping any sequence(s) o strings: are considered equal if, after unescaping any sequence(s)
in both strings starting with a reverse solidus, they contain the in both strings starting with a reverse solidus, they contain the
same number of Unicode characters and their code points are same number of Unicode characters and their code points are
position-wise equal. position-wise equal.
o numbers: are considered equal if subtracting one from the other o numbers: are considered equal if subtracting one from the other
results in 0. results in 0.
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See [RFC5789], Section 2.2 for considerations regarding handling See [RFC5789], Section 2.2 for considerations regarding handling
errors when JSON Patch is used with the HTTP PATCH method, including errors when JSON Patch is used with the HTTP PATCH method, including
suggested status codes to use to indicate various conditions. suggested status codes to use to indicate various conditions.
Note that as per [RFC5789], when used with the PATCH HTTP method, it Note that as per [RFC5789], when used with the PATCH HTTP method, it
is atomic. Therefore, the following patch would result in no changes is atomic. Therefore, the following patch would result in no changes
being made to the document at all (because the "test" operation being made to the document at all (because the "test" operation
results in an error). results in an error).
[ [
{ "op": "replace", "path": "/a/b/c", "value": 42 }, { "op": "replace", "path": "/a/b/c", "value": 42 },
{ "op": "test", "path": "/a/b/c", "value": "C" } { "op": "test", "path": "/a/b/c", "value": "C" }
] ]
6. IANA Considerations 6. IANA Considerations
The Internet media type for a JSON Patch document is application/ The Internet media type for a JSON Patch document is application/
json-patch. json-patch.
Type name: application Type name: application
Subtype name: json-patch Subtype name: json-patch
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[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP", [RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010. RFC 5789, March 2010.
Appendix A. Examples Appendix A. Examples
A.1. Adding an Object Member A.1. Adding an Object Member
An example target JSON document: An example target JSON document:
{ {
"foo": "bar" "foo": "bar"
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "add", "path": "/baz", "value": "qux" } { "op": "add", "path": "/baz", "value": "qux" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"baz": "qux", "baz": "qux",
"foo": "bar" "foo": "bar"
} }
A.2. Adding an Array Element A.2. Adding an Array Element
An example target JSON document: An example target JSON document:
{ {
"foo": [ "bar", "baz" ] "foo": [ "bar", "baz" ]
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "add", "path": "/foo/1", "value": "qux" } { "op": "add", "path": "/foo/1", "value": "qux" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"foo": [ "bar", "qux", "baz" ] "foo": [ "bar", "qux", "baz" ]
} }
A.3. Removing an Object Member A.3. Removing an Object Member
An example target JSON document: An example target JSON document:
{ {
"baz": "qux", "baz": "qux",
"foo": "bar" "foo": "bar"
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "remove", "path": "/baz" } { "op": "remove", "path": "/baz" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"foo": "bar" "foo": "bar"
} }
A.4. Removing an Array Element A.4. Removing an Array Element
An example target JSON document: An example target JSON document:
{ {
"foo": [ "bar", "qux", "baz" ] "foo": [ "bar", "qux", "baz" ]
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "remove", "path": "/foo/1" } { "op": "remove", "path": "/foo/1" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"foo": [ "bar", "baz" ] "foo": [ "bar", "baz" ]
} }
A.5. Replacing a Value A.5. Replacing a Value
An example target JSON document: An example target JSON document:
{ {
"baz": "qux", "baz": "qux",
"foo": "bar" "foo": "bar"
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "replace", "path": "/baz", "value": "boo" } { "op": "replace", "path": "/baz", "value": "boo" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"baz": "boo", "baz": "boo",
"foo": "bar" "foo": "bar"
} }
A.6. Moving a Value A.6. Moving a Value
An example target JSON document: An example target JSON document:
{ {
"foo": { "foo": {
"bar": "baz", "bar": "baz",
"waldo": "fred" "waldo": "fred"
} }
"qux": { "qux": {
"corge": "grault" "corge": "grault"
} }
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "move", "path": "/foo/waldo", to: "/qux/thud" } { "op": "move", "path": "/foo/waldo", to: "/qux/thud" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"foo": { "foo": {
"bar": "baz" "bar": "baz"
} }
"qux": { "qux": {
"corge": "grault", "corge": "grault",
"thud": "fred" "thud": "fred"
} }
} }
A.7. Moving an Array Element A.7. Moving an Array Element
An example target JSON document: An example target JSON document:
{ {
"foo": [ "all", "grass", "cows", "eat" ] "foo": [ "all", "grass", "cows", "eat" ]
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "move", "path": "/foo/1", "to": "/foo/3" } { "op": "move", "path": "/foo/1", "to": "/foo/3" }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"foo": [ "all", "cows", "eat", "grass" ] "foo": [ "all", "cows", "eat", "grass" ]
} }
A.8. Testing a Value: Success A.8. Testing a Value: Success
An example target JSON document: An example target JSON document:
{ {
"baz": "qux", "baz": "qux",
"foo": [ "a", 2, "c" ] "foo": [ "a", 2, "c" ]
} }
A JSON Patch document that will result in successful evaluation: A JSON Patch document that will result in successful evaluation:
[ [
{ "op": "test", "path": "/baz", "value": "qux" }, { "op": "test", "path": "/baz", "value": "qux" },
{ "op": "test", "path": "/foo/1", "value": 2 } { "op": "test", "path": "/foo/1", "value": 2 }
] ]
A.9. Testing a Value: Error A.9. Testing a Value: Error
An example target JSON document: An example target JSON document:
{ {
"baz": "qux" "baz": "qux"
} }
A JSON Patch document that will result in an error condition: A JSON Patch document that will result in an error condition:
[ [
{ "op": "test", "path": "/baz", "value": "bar" } { "op": "test", "path": "/baz", "value": "bar" }
] ]
A.10. Adding a nested Member Object A.10. Adding a nested Member Object
An example target JSON document: An example target JSON document:
{ {
"foo": "bar" "foo": "bar"
} }
A JSON Patch document: A JSON Patch document:
[ [
{ "op": "add", "path": "/child", "value": { "grandchild": { } } } { "op": "add", "path": "/child", "value": { "grandchild": { } } }
] ]
The resulting JSON document: The resulting JSON document:
{ {
"foo": "bar", "foo": "bar",
"child": { "child": {
"grandchild": { "grandchild": {
} }
} }
} }
A.11. Ignoring Unrecognized Elements
An example target JSON document:
{
"foo":"bar"
}
A JSON Patch document:
[
{ "op":"add", "path":"/baz", "value":"qux", "xyz":123 }
]
The resulting JSON document:
{
"foo":"bar",
"baz":"qux"
}
A.12. Adding to a Non-existant Target
An example target JSON document:
{
"foo": "bar"
}
A JSON Patch document:
[
{ "op": "add", "path": "/baz/bat", "value": "qux" }
]
This JSON Patch document, applied to the target JSON document above,
would result in an error (therefore not being applied) because the
"add" operation's target location that references neither the root of
the document, nor a member of an existing object, nor a member of an
existing array.
A.13. Invalid JSON Patch Document
A JSON Patch document:
[
{ "op":"add", "path":"/baz", "value":"qux", "op":"remove" }
]
This JSON Patch document cannot be treated as an "add" operation
since there is a later "op":"remove" element. A JSON parser that
hides such duplicate element names therefore cannot be used unless it
always exposes only the last element with a given name (eg
"op":"remove" in this example).
Authors' Addresses Authors' Addresses
Paul C. Bryan (editor) Paul C. Bryan (editor)
Salesforce.com Salesforce.com
Phone: +1 604 783 1481 Phone: +1 604 783 1481
Email: pbryan@anode.ca Email: pbryan@anode.ca
Mark Nottingham (editor) Mark Nottingham (editor)
 End of changes. 56 change blocks. 
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