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<title>Decentralized Identifiers (DIDs) v1.0</title>
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<body data-cite="infra rfc3986">
<section id='abstract'>
<p>
<a>Decentralized identifiers</a> (DIDs) are a new type of identifier that
enables verifiable, decentralized digital identity. A <a>DID</a> refers to any
subject (e.g., a person, organization, thing, data model, abstract entity, etc.)
as determined by the controller of the <a>DID</a>. In contrast to
typical, federated identifiers, <a>DIDs</a> have been designed so that they may
be decoupled from centralized registries, identity providers, and certificate
authorities. Specifically, while other parties might be used to help enable the
discovery of information related to a <a>DID</a>, the design enables the
controller of a <a>DID</a> to prove control over it without requiring permission
from any other party. <a>DIDs</a> are <a>URIs</a> that associate a <a>DID
subject</a> with a <a>DID document</a> allowing trustable interactions
associated with that subject.
</p>
<p>
Each <a>DID document</a> can express cryptographic material, <a>verification
methods</a>, or <a>services</a>, which provide a set of mechanisms enabling a
<a>DID controller</a> to prove control of the <a>DID</a>. <a>Services</a> enable
trusted interactions associated with the <a>DID subject</a>. A <a>DID</a> might
provide the means to return the <a>DID subject</a> itself, if the <a>DID
subject</a> is an information resource such as a data model.
</p>
<p>
This document specifies the DID syntax, a common data model, core properties,
serialized representations, DID operations, and an explanation of the process
of resolving DIDs to the resources that they represent.
</p>
</section>
<section id='sotd'>
<p>
The W3C Decentralized Identifier Working Group has published this document as a
W3C Candidate Recommendation and is requesting that software developers and DID
Method specification authors provide experimental implementations designed to
test the implementability of all of the features in this document.
</p>
<p>
To exit the W3C Candidate Recommendation phase, the W3C DID Working Group will
require two things: 1) for normative statements that are machine testable, at
least two interoperable implementations per feature, and 2) for normative
statements that are not machine testable, at least two demonstrations of
implementation per feature. A feature is defined as one or more functionally
related normative statements in the specification.
</p>
<p>
At present, there exist
<a href="https://w3c-ccg.github.io/did-method-registry/#did-methods">98
experimental DID Method specifications</a>, 32 experimental DID Method driver
implementations, a Candidate Recommendation <a
href="https://w3c.github.io/did-test-suite/">test suite</a> that determines
whether or not a given implementation is conformant with this specification
and 18 implementations submitted to the conformance test suite.
Readers are advised to heed the <a
href="https://github.com/w3c/did-core/issues">DID Core issues</a> and <a
href="https://github.com/w3c/did-test-suite/issues"> DID Core Test Suite
issues</a> that each contain the latest list of concerns and proposed changes
that might result in alterations to this specification.
</p>
<p>
Changes since the <a
href="https://www.w3.org/TR/2021/CR-did-core-20210318/">First Candidate
Recommendation</a> include:
</p>
<ul>
<li>
Addition of at risk markers to most of the DID Parameters, the data model
datatypes that are expected to not be implemented, and the
application/did+ld+json media type. This change resulted in the DID WG's
decision to perform a second Candidate Recommendation phase. All other
changes were either editorial or predicted in "at risk" issue markers.
</li>
<li>
Removal of the at risk issue marker for the `method-specific-id` ABNF rule
and for `nextUpdate` and `nextVersionId`.
</li>
<li>
Clarification that `equivalentId` and `canonicalId` are optional.
</li>
<li>
Addition of a definitions for "amplification attack" and "cryptographic suite".
</li>
<li>
Replacing the use of `publicKeyBase58` with `publicKeyMultibase`.
</li>
<li>
Updates to the DID Document examples section.
</li>
<li>
A large number of editorial clean ups to the Security Considerations section.
</li>
</ul>
<p>
Changes since the <a
href="https://www.w3.org/TR/2019/WD-did-core-20191107/">First Public Working
Draft</a> include:
</p>
<ul>
<li>
The introduction of an abstract data model that can be serialized to multiple
representations including JSON and JSON-LD.
</li>
<li>
The introduction of a DID Specifications Registry for the purposes of
registering extension properties, representations, DID Resolution input
metadata and output metadata, DID Document metadata, DID parameters, and DID
Methods.
</li>
<li>
Separation of DID Document metadata, such as created and updated values,
from DID Document properties.
</li>
<li>
The removal of embedded proofs in the DID Document.
</li>
<li>
The addition of verification relationships for the purposes of authentication,
assertion, key agreement, capability invocation and capability delegation.
</li>
<li>
The ability to support relating multiple identifiers with the DID Document,
such as the DID controller, also known as, equivalent IDs, and canonical IDs.
</li>
<li>
Enhancing privacy by reducing information that could contain personally
identifiable information in the DID Document.
</li>
<li>
The addition of a large section on security considerations and privacy
considerations.
</li>
<li>
A Representations section that details how the abstract data model can be
produced and consumed in a variety of different formats along with general
rules for all representations, producers, and consumers.
</li>
<li>
A section detailing the DID Resolution and DID URL Dereferencing interface
definition that all DID resolvers are expected to expose as well as inputs
and outputs to those processes.
</li>
<li>
DID Document examples in an appendix that provide more complex examples of
DID Document serializations.
</li>
<li>
IANA Considerations for multiple representations specified in DID Core.
</li>
<li>
Removal of the Future Work section as much of the work has now been
accomplished.
</li>
<li>
An acknowledgements section.
</li>
</ul>
<p>
Comments regarding this document are welcome. Please file issues
directly on <a href="https://github.com/w3c/did-core/issues/">GitHub</a>,
or send them
to <a href="mailto:public-did-wg@w3.org">public-did-wg@w3.org</a> (
<a href="mailto:public-did-wg-request@w3.org?subject=subscribe">subscribe</a>,
<a href="https://lists.w3.org/Archives/Public/public-did-wg/">archives</a>).
</p>
</section>
<section class="informative">
<h1>Introduction</h1>
<p>
As individuals and organizations, many of us use globally unique identifiers in
a wide variety of contexts. They serve as communications addresses (telephone
numbers, email addresses, usernames on social media), ID numbers (for passports,
drivers licenses, tax IDs, health insurance), and product identifiers (serial
numbers, barcodes, RFIDs). URIs (Uniform Resource Identifiers) are used for
resources on the Web and each web page you view in a browser has a globally
unique URL (Uniform Resource Locator).
</p>
<p>
The vast majority of these globally unique identifiers are not under our
control. They are issued by external authorities that decide who or what they
refer to and when they can be revoked. They are useful only in certain contexts
and recognized only by certain bodies not of our choosing. They might
disappear or cease to be valid with the failure of an organization. They might
unnecessarily reveal personal information. In many cases, they can be
fraudulently replicated and asserted by a malicious third-party, which is
more commonly known as "identity theft".
</p>
<p>
The Decentralized Identifiers (DIDs) defined in this specification are a new
type of globally unique identifier. They are designed to enable individuals and
organizations to generate their own identifiers using systems they trust. These
new identifiers enable entities to prove control over them by authenticating
using cryptographic proofs such as digital signatures.
</p>
<p>
Since the generation and assertion of Decentralized Identifiers is
entity-controlled, each entity can have as many DIDs as necessary to maintain
their desired separation of identities, personas, and interactions. The use of
these identifiers can be scoped appropriately to different contexts. They
support interactions with other people, institutions, or systems that require
entities to identify themselves, or things they control, while providing control
over how much personal or private data should be revealed, all without depending
on a central authority to guarantee the continued existence of the identifier.
</p>
<p>
This specification does not presuppose any particular technology or cryptography
to underpin the generation, persistence, resolution, or interpretation of DIDs.
For example, implementers can create Decentralized Identifiers based on
identifiers registered in federated or centralized identity management systems.
Indeed, almost all types of identifier systems can add support for DIDs. This
creates an interoperability bridge between the worlds of centralized, federated,
and decentralized identifiers. This also enables implementers to design specific
types of DIDs to work with the computing infrastructure they trust, such as
distributed ledgers, decentralized file systems, distributed databases, and
peer-to-peer networks.
</p>
<p>
This specification is for:
</p>
<ul>
<li>
Anyone that wants to understand the core architectural principles that
are the foundation for Decentralized Identifiers;
</li>
<li>
Software developers that want to produce and consume Decentralized Identifiers
and their associated data formats;
</li>
<li>
Systems integrators that want to understand how to use Decentralized
Identifiers in their software and hardware systems;
</li>
<li>
Specification authors that want to create new DID infrastructures, known as DID
methods, that conform to the ecosystem described by this document.
</li>
</ul>
<p>
In addition to this specification, readers might find the
Use Cases and Requirements for Decentralized Identifiers [[DID-USE-CASES]]
document useful.
</p>
<section class="informative">
<h2>A Simple Example</h2>
<p>
A <a>DID</a> is a simple text string consisting of three parts: 1) the
<code>did</code> URI scheme identifier, 2) the identifier for the <a>DID
method</a>, and 3) the DID method-specific identifier.
</p>
<figure id="parts-of-a-did">
<img style="margin: auto; display: block; width: 75%;"
src="diagrams/parts-of-a-did.svg" alt="
A diagram showing the parts of a DID. The left-most letters spell 'did' in blue,
are enclosed in a horizontal bracket from above and a label that reads 'scheme'
above the bracket. A gray colon follows the 'did' letters. The middle letters
spell 'example' in magenta, are enclosed in a horizontal bracket from below and
a label that reads 'DID Method' below the bracket. A gray colon follows the
DID Method. Finally, the letters at the end read '123456789abcdefghi' in
green, are enclosed in a horizontal bracket from below and a label that
reads 'DID Method Specific String' below the bracket.
" >
<figcaption>
A simple example of a decentralized identifier (DID)
</figcaption>
</figure>
<p>
The example <a>DID</a> above resolves to a <a>DID document</a>. A <a>DID
document</a> contains information associated with the <a>DID</a>, such as ways
to cryptographically <a>authenticate</a> a <a>DID controller</a>.
</p>
<pre class="example nohighlight" title="A simple DID document">
{
"@context": [
"https://www.w3.org/ns/did/v1",
"https://w3id.org/security/suites/ed25519-2020/v1"
]
"id": "did:example:123456789abcdefghi",
"authentication": [{
<span class="comment">// used to authenticate as did:...fghi</span>
"id": "did:example:123456789abcdefghi#keys-1",
"type": "Ed25519VerificationKey2020",
"controller": "did:example:123456789abcdefghi",
"publicKeyMultibase": "zH3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
}]
}
</pre>
</section>
<section class="informative">
<h2>Design Goals</h2>
<p>
<a>Decentralized Identifiers</a> are a component of larger systems, such as the
Verifiable Credentials ecosystem [[VC-DATA-MODEL]], which influenced the design
goals for this specification. The design goals for Decentralized Identifiers
are summarized here.
</p>
<table class="simple">
<thead>
<tr>
<th>
Goal
</th>
<th>
Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
Decentralization
</td>
<td>
Eliminate the requirement for centralized authorities or single point failure in
identifier management, including the registration of globally unique
identifiers, public verification keys, <a>services</a>, and other information.
</td>
</tr>
<tr>
<td>
Control
</td>
<td>
Give entities, both human and non-human, the power to directly control their
digital identifiers without the need to rely on external authorities.
</td>
</tr>
<tr>
<td>
Privacy
</td>
<td>
Enable entities to control the privacy of their information, including minimal,
selective, and progressive disclosure of attributes or other data.
</td>
</tr>
<tr>
<td>
Security
</td>
<td>
Enable sufficient security for requesting parties to depend on <a>DID
documents</a> for their required level of assurance.
</td>
</tr>
<tr>
<td>
Proof-based
</td>
<td>
Enable <a>DID controllers</a> to provide cryptographic proof when interacting
with other entities.
</td>
</tr>
<tr>
<td>
Discoverability
</td>
<td>
Make it possible for entities to discover <a>DIDs</a> for other entities, to
learn more about or interact with those entities.
</td>
</tr>
<tr>
<td>
Interoperability
</td>
<td>
Use interoperable standards so <a>DID</a> infrastructure can make use of
existing tools and software libraries designed for interoperability.
</td>
</tr>
<tr>
<td>
Portability
</td>
<td>
Be system- and network-independent and enable entities to use their digital
identifiers with any system that supports <a>DIDs</a> and <a>DID methods</a>.
</td>
</tr>
<tr>
<td>
Simplicity
</td>
<td>
Favor a reduced set of simple features to make the technology easier to
understand, implement, and deploy.
</td>
</tr>
<tr>
<td>
Extensibility
</td>
<td>
Where possible, enable extensibility provided it does not greatly hinder
interoperability, portability, or simplicity.
</td>
</tr>
</tbody>
</table>
</section>
<section class="informative">
<h2>
Architecture Overview
</h2>
<p>
This section provides a basic overview of the major components of
Decentralized Identifier architecture.
</p>
<figure id="brief-architecture-overview">
<img style="margin: auto; display: block; width: 75%;"
src="diagrams/did_brief_architecture_overview.svg" alt="
DIDs and DID documents are recorded on a Verifiable Data Registry; DIDs resolve
to DID documents; DIDs refer to DID subjects; a DID controller controls a DID
document; DID URLs contains a DID; DID URLs dereferenced to DID document
fragments or external resources.
" >
<figcaption>
Overview of DID architecture and the relationship of the basic components.
</figcaption>
</figure>
<dl>
<dt>
DIDs and DID URLs
</dt>
<dd>
A Decentralized Identifier, or <a>DID</a>, is a <a>URI</a> composed of three
parts: the scheme <code>did:</code>, a method identifier, and a unique,
method-specific identifier specified by the <a>DID method</a>. <a>DIDs</a> are
resolvable to <a>DID documents</a>. A <a>DID URL</a> extends the syntax of a
basic <a>DID</a> to incorporate other standard <a>URI</a> components such as
path, query, and fragment in order to locate a particular
<a>resource</a>—for example, a cryptographic public key inside a <a>DID
document</a>, or a <a>resource</a> external to the <a>DID document</a>.
These concepts are elaborated upon in <a href="#did-syntax"></a> and <a
href="#did-url-syntax"></a>.
</dd>
<dt>
DID subjects
</dt>
<dd>
The subject of a <a>DID</a> is, by definition, the entity identified by the
<a>DID</a>. The <a>DID subject</a> might also be the <a>DID controller</a>.
Anything can be the subject of a <a>DID</a>: person, group, organization,
thing, or concept. This is further defined in <a href="#did-subject"></a>.
</dd>
<dt>
DID controllers
</dt>
<dd>
The <a>controller</a> of a <a>DID</a> is the entity (person, organization, or
autonomous software) that has the capability—as defined by a <a>DID
method</a>—to make changes to a <a>DID document</a>. This capability is
typically asserted by the control of a set of cryptographic keys used by
software acting on behalf of the controller, though it might also be asserted
via other mechanisms. Note that a <a>DID</a> might have more than one
controller, and the <a>DID subject</a> can be the <a>DID controller</a>, or one
of them. This concept is documented in <a href="#did-controller"></a>.
</dd>
<dt>
Verifiable data registries
</dt>
<dd>
In order to be resolvable to <a>DID documents</a>, <a>DIDs</a> are typically
recorded on an underlying system or network of some kind. Regardless of the
specific technology used, any such system that supports recording <a>DIDs</a>
and returning data necessary to produce <a>DID documents</a> is called a
<a>verifiable data registry</a>. Examples include <a>distributed ledgers</a>,
decentralized file systems, databases of any kind, peer-to-peer networks, and
other forms of trusted data storage. This concept is further elaborated upon in
<a href="#methods"></a>.
</dd>
<dt>
DID documents
</dt>
<dd>
<a>DID documents</a> contain information associated with a <a>DID</a>. They
typically express <a>verification methods</a>, such as cryptographic public
keys, and <a>services</a> relevant to interactions with the <a>DID subject</a>.
The generic properties supported in a <a>DID document</a> are specified in <a
href="#core-properties"></a>. A <a>DID document</a> can be serialized to a byte
stream (see <a href="#representations"></a>). The properties present in
a <a>DID document</a> can be updated according to the applicable operations
outlined in <a href="#methods"></a>.
</dd>
<dt>
DID methods
</dt>
<dd>
<a>DID methods</a> are the mechanism by which a particular type of <a>DID</a>
and its associated <a>DID document</a> are created, resolved, updated, and
deactivated. <a>DID methods</a> are defined using separate DID method
specifications as defined in <a href="#methods"></a>.
</dd>
<dt>
DID resolvers and DID resolution
</dt>
<dd>
A <a>DID resolver</a> is a system component that takes a <a>DID</a> as input and
produces a conforming <a>DID document</a> as output. This process is called
<a>DID resolution</a>. The steps for resolving a specific type of <a>DID</a> are
defined by the relevant <a>DID method</a> specification. The process of <a>DID
resolution</a> is elaborated upon in <a href="#resolution"></a>.
</dd>
<dt>
DID URL dereferencers and DID URL dereferencing
</dt>
<dd>
A <a>DID URL dereferencer</a> is a system component that takes a <a>DID URL</a>
as input and produces a <a>resource</a> as output. This process is
called <a>DID URL dereferencing</a>. The process of <a>DID URL dereferencing</a>
is elaborated upon in <a href="#did-url-dereferencing"></a>.
</dd>
</dl>
</section>
<section id="conformance">
<p>
This document contains examples that contain JSON and JSON-LD content.
Some of these examples contain characters that are invalid, such as inline
comments (<code>//</code>) and the use of ellipsis (<code>...</code>) to denote
information that adds little value to the example. Implementers are cautioned to
remove this content if they desire to use the information as valid JSON
or JSON-LD.
</p>
<p>
Some examples contain terms, both property names and values, that are not
defined in this specification. These are indicated with a comment (<code>//
external (property name|value)</code>). Such terms, when used in a <a>DID
document</a>, are expected to be registered in the DID Specification Registries
[[?DID-SPEC-REGISTRIES]] with links to both a formal definition and a JSON-LD
context.
</p>
<p>
Interoperability of implementations for <a>DIDs</a> and <a>DID documents</a> is
tested by evaluating an implementation's ability to create and parse <a>DIDs</a>
and <a>DID documents</a> that conform to this specification. Interoperability
for producers and consumers of <a>DIDs</a> and <a>DID documents</a> is provided
by ensuring the <a>DIDs</a> and <a>DID documents</a> conform. Interoperability
for <a>DID method</a> specifications is provided by the details in each <a>DID
method</a> specification. It is understood that, in the same way that a web
browser is not required to implement all known <a>URI</a> schemes, conformant
software that works with <a>DIDs</a> is not required to implement all known
<a>DID methods</a>. However, all implementations of a given <a>DID method</a>
are expected to be interoperable for that method.
</p>
<p>
A <dfn>conforming DID</dfn> is any concrete expression of the rules specified in
<a href="#identifier"></a> which complies with relevant normative statements in
that section.
</p>
<p>
A <dfn>conforming DID document</dfn> is any concrete expression of the data
model described in this specification which complies with the relevant normative
statements in <a href="#data-model"></a> and <a href="#core-properties"></a>. A
serialization format for the conforming document is deterministic,
bi-directional, and lossless, as described in <a href="#representations"></a>.
</p>
<p>
A <dfn>conforming producer</dfn> is any algorithm realized as software and/or
hardware that generates <a>conforming DIDs</a> or <a>conforming DID
Documents</a> and complies with the relevant normative statements in <a
href="#representations"></a>.
</p>
<p>
A <dfn>conforming consumer</dfn> is any algorithm realized as software and/or
hardware that consumes <a>conforming DIDs</a> or <a>conforming DID documents</a>
and complies with the relevant normative statements in <a
href="#representations"></a>.
</p>
<p>
A <dfn>conforming DID resolver</dfn> is any algorithm realized as software
and/or hardware that complies with the relevant normative statements in
<a href="#did-resolution"></a>.
</p>
<p>
A <dfn>conforming DID URL dereferencer</dfn> is any algorithm realized as
software and/or hardware that complies with the relevant normative statements in
<a href="#did-url-dereferencing"></a>.
</p>
<p>
A <dfn>conforming DID method</dfn> is any specification that complies with the
relevant normative statements in <a href="#methods"></a>.
</p>
</section>
</section>
<section class="informative">
<h2>Terminology</h2>
<div data-include="terms.html">
</div>
<p>
In addition to the terminology above, this specification also uses terminology
from the [[INFRA]] specification to formally define the <a
href="#data-model">data model</a>. When [[INFRA]] terminology is used, such as
<a data-cite="INFRA#strings">string</a>, <a
data-cite="INFRA#ordered-set">set</a>, and <a
data-cite="INFRA#maps">map</a>, it is linked directly to that specification.
</p>
</section>
<section>
<h2>Identifier</h2>
<p>
This section describes the formal syntax for <a>DIDs</a> and <a>DID URLs</a>.
The term "generic" is used to differentiate the syntax defined here from syntax
defined by <em>specific</em> <a>DID methods</a> in their respective
specifications. The creation processes, and their timing, for <a>DIDs</a> and
<a>DID URLs</a> are described in <a href="#method-operations"></a> and
<a href="#creation-of-a-did"></a>.
</p>
<section class="normative">
<h3>DID Syntax</h3>
<p>
The generic <a>DID scheme</a> is a <a>URI</a> scheme conformant with
[[!RFC3986]]. The ABNF definition can be found below, which uses the syntax in
[[!RFC5234]] and the corresponding definitions for <code>ALPHA</code> and
<code>DIGIT</code>. All other rule names not defined in the ABNF below are
defined in [[RFC3986]]. All <a>DIDs</a> MUST conform to the
DID Syntax ABNF Rules.
</p>
<table class="simple">
<thead>
<tr>
<th>
The DID Syntax ABNF Rules
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<pre class="nohighlight">
did = "did:" method-name ":" method-specific-id
method-name = 1*method-char
method-char = %x61-7A / DIGIT
method-specific-id = *( *idchar ":" ) 1*idchar
idchar = ALPHA / DIGIT / "." / "-" / "_" / pct-encoded
pct-encoded = "%" HEXDIG HEXDIG
</pre>
</td>
</tr>
</tbody>
</table>
<p>
For requirements on <a>DID methods</a> relating to the <a>DID</a> syntax, see
Section <a href="#method-syntax"></a>.
</p>
</section>
<section class="normative">
<h3>DID URL Syntax</h3>
<p>
A <a>DID URL</a> is a network location identifier for a specific
<a>resource</a>. It can be used to retrieve things like representations
of <a>DID subjects</a>, <a>verification methods</a>, <a>services</a>,
specific parts of a <a>DID document</a>, or other resources.
</p>
<p>
The following is the ABNF definition using the syntax in [[!RFC5234]]. It builds
on the <code>did</code> scheme defined in <a href="#did-syntax"></a>. The <a
data-cite="!rfc3986#section-3.3"><code>path-abempty</code></a>, <a
data-cite="!rfc3986#section-3.4"><code>query</code></a>, and <a
data-cite="!rfc3986#section-3.5"><code>fragment</code></a> components are
defined in [[!RFC3986]]. All <a>DID URLs</a> MUST conform to the
DID URL Syntax ABNF Rules. <a>DID methods</a> can further restrict these
rules, as described in <a href="#method-syntax"></a>.
</p>
<table class="simple">
<thead>
<tr>
<th>
The DID URL Syntax ABNF Rules
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<pre class="nohighlight">
did-url = did path-abempty [ "?" query ] [ "#" fragment ]
</pre>
</td>
</tr>
</tbody>
</table>
<p class="note" title="Semicolon character is reserved for future use">
Although the semicolon (<code>;</code>) character can be used according to the
rules of the <a>DID URL</a> syntax, future versions of this specification may
use it as a sub-delimiter for parameters as described in [[?MATRIX-URIS]]. To
avoid future conflicts, developers ought to refrain from using it.
</p>
<section class="notoc">
<h2>Path</h2>
<p>
A <a>DID path</a> is identical to a generic <a>URI</a> path and conforms to the
<code>path-abempty</code> ABNF rule in <a
data-cite="RFC3986#section-3.3">RFC 3986, section 3.3</a>. As with
<a>URIs</a>, path semantics can be specified by <a>DID Methods</a>, which in
turn might enable <a>DID controllers</a> to further specialize those semantics.
</p>
<pre class="example nohighlight">
did:example:123456/path
</pre>
</section>
<section class="notoc">
<h2>Query</h2>
<p>
A <a>DID query</a> is identical to a generic <a>URI</a> query and conforms to
the <code>query</code> ABNF rule in <a
data-cite="RFC3986#section-3.4">RFC 3986, section 3.4</a>. This syntax
feature is elaborated upon in <a href="#did-parameters"></a>.
</p>
<pre class="example nohighlight">
did:example:123456?versionId=1
</pre>
</section>
<section class="notoc">
<h2>Fragment</h2>
<p>
<a>DID fragment</a> syntax and semantics are identical to a generic <a>URI</a>
fragment and conforms to the <code>fragment</code> ABNF rule in <a
data-cite="RFC3986#section-3.5">RFC 3986, section 3.5</a>.
</p>
<p>
A <a>DID fragment</a> is used as a method-independent reference into a <a>DID
document</a> or external <a>resource</a>. Some examples of DID fragment
identifiers are shown below.
</p>
<pre class="example nohighlight"
title="A unique verification method in a DID Document">
did:example:123#public-key-0
</pre>
<pre class="example nohighlight"
title="A unique service in a DID Document">
did:example:123#agent
</pre>
<pre class="example nohighlight"
title="A resource external to a DID Document">