pdns-qof/i-d/pdns-qof.xml

<?xml version="1.0" encoding="utf-8"?>
<?xml-model href="rfc7991bis.rnc"?>  <!-- Required for schema validation and schema-aware editing -->
<?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?>

<!DOCTYPE rfc [

  <!ENTITY RFC1034 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.1034.xml">
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  <!ENTITY RFC3597 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3597.xml">
  <!ENTITY RFC3912 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3912.xml">
  <!ENTITY RFC3986 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3986.xml">
  <!ENTITY RFC4627 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4627.xml">
  <!ENTITY RFC6648 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6648.xml">
  <!ENTITY RFC6973 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6973.xml">
  <!ENTITY RFC7258 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.7258.xml">
  <!ENTITY RFC7871 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.7871.xml">
  <!ENTITY I-D.narten-iana-considerations-rfc2434bis SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.narten-iana-considerations-rfc2434bis.xml">
  <!ENTITY I-D.draft-bortzmeyer-dnsop-dns-privacy SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-bortzmeyer-dnsop-dns-privacy">
]>


<rfc
  xmlns:xi="http://www.w3.org/2001/XInclude"
  category="info"
  docName="draft-dulaunoy-dnsop-passive-dns-cof-12"
  ipr="trust200902"
  obsoletes=""
  updates=""
  submissionType="IETF"
  xml:lang="en"
  version="3">

  <!-- ***** FRONT MATTER ***** -->
  <front>
    <title abbrev="Passive DNS - Common Output Format">Passive DNS - Common Output Format</title>
    <author fullname="Alexandre Dulaunoy" initials="A." surname="Dulaunoy">
      <organization>CIRCL</organization>
      <address>
        <postal>
          <street>122, rue Adolphe Fischer</street>
          <city>Luxembourg</city>
          <region />
          <code>L-1521</code>
          <country>Luxembourg</country>
        </postal>
        <phone>(+352) 247 88444</phone>
        <email>alexandre.dulaunoy@circl.lu</email>
        <uri>http://www.circl.lu/</uri>
        <!-- uri and facsimile elements may also be added -->
      </address>
    </author>
    <author fullname="L. Aaron Kaplan" initials="A." surname="Kaplan">
      <organization />
      <address>
        <postal>
          <street>
          </street>
          <city>Vienna</city>
          <region />
          <code>A-1170</code>
          <country>Austria</country>
        </postal>
        <phone />
        <email>aaron@lo-res.org</email>
        <uri />
      </address>
    </author>
    <author fullname="Paul Vixie" initials="P." surname="Vixie">
      <organization>Farsight Security, Inc.</organization>
      <address>
        <postal>
          <street>11400 La Honda Road</street>
          <city>Woodside</city>
          <region>California</region>
          <code>94062</code>
          <country>USA</country>
        </postal>
        <phone />
        <email>paul@redbarn.org</email>
        <uri>https://www.farsightsecurity.com/</uri>
      </address>
    </author>
    <author fullname="Henry Stern" initials="H." surname="Stern">
      <organization>Farsight Security, Inc.</organization>
      <address>
        <postal>
          <street>11400 La Honda Road</street>
          <city>Woodside</city>
          <region>California</region>
          <code>94062</code>
          <country>USA</country>
        </postal>
        <phone>+1 650 542-7836</phone>
        <email>henry@stern.ca</email>
        <uri>https://www.farsightsecurity.com/</uri>
      </address>
    </author>
    <author initials="W." surname="Kumari" fullname="Warren Kumari">
      <organization>Google</organization>
      <address>
        <email>warren@kumari.net</email>
      </address>
    </author>

    <date day="27" month="August" year="2024" />
    <area>General</area>
    <workgroup>Domain Name System Operations</workgroup>
    <keyword>dns</keyword>
    <abstract>
      <t>This document describes a common output format of Passive DNS servers that clients can
        query. The output format description also includes a common semantic for each Passive DNS
        system. By having multiple Passive DNS Systems adhere to the same output format for queries,
        users of multiple Passive DNS servers will be able to combine result sets easily.</t>
    </abstract>
  </front>
  <middle>
    <section title="Introduction">
      <t>Passive DNS is a technique described by Florian Weimer in 2005 in <xref target="WEIMERPDNS">Passive
        DNS replication, F Weimer - 17th Annual FIRST Conference on Computer Security</xref>.
        It is a mechanism for
      logging DNS answers in a manner intended to minimize the privacy
      implications to users, and is widely by security researchers to investigate
      malware (for example to discover command and control servers), and other
      security threats. By capturing only the "cache fill" DNS responses
      (responses from authoritative servers in response to queries performed by a
      recursive resolver when iteratively resolving a name), Passive DNS does
      not have access to the client (users) source IP, source port, destination
      IP, or destination port.</t>

      <t>As these answers are served in response to queries originally
      initiated by user devices, the Passive DNS data can be used to detect if
      devices using the resolver are connecting to known malicious domains,
      without identifying the individual users / devices. In addition, as
      answers are responses to queries made by the recursive server itself,
      Passive DNS records the answers which are ultimately served to users.
      This is important as authoritative servers may serve different answers to
      different query addresses, for example to increase performance (e.g <xref
      target="RFC7871">Client Subnet in DNS Queries</xref>) or to hide
      malicious behavior when queried from addresses known to be associated
      with security researchers.</t>

      <t>Passive DNS is usually implemented either by capturing DNS response
        packets themselves (i.e packets with a destination address of the
        recursive resolver, a source port of 53, and the QR bit set to 1) or
        by having the DNS software itself log these responses. The latter method
        is likely to become more common as recursive to authoritative DNS
        communication becomes encrypted.
      </t>

      <t>Multiple Passive DNS implementations and services exist. Users of
      these Passive DNS services may query a server (often via <xref
      target="RFC3912">WHOIS</xref>
      or HTTP <xref target="REST">REST</xref>), parse the results, and process
      them in other applications. Users of Passive DNS query each
      implementation and aggregate the results for their search. This document
      describes the output format of four Passive DNS Systems (<xref
      target="DNSDB" />, <xref target="DNSDBQ" />,
      <xref target="PDNSCIRCL" /> and <xref target="PDNSCOF" />) that are
      in use today and that already share a nearly identical output format. As
      the format and the meaning of output fields from each Passive DNS need to
      be consistent, this document proposes a solution to commonly name each
      field along with its corresponding interpretation. The format follows a
      simple key-value structure in <xref target="RFC4627">JSON</xref>
        format. The benefit of having a consistent Passive DNS output format is
        that multiple client implementations can query different servers
        without having to have a separate parser for each individual server.
        <xref target="PDNSCLIENT">passivedns-client</xref> currently implements
        multiple parsers due to a lack of standardization. The document does
        not describe the protocol (e.g. <xref target="RFC3912">WHOIS</xref>,
        HTTP <xref target="REST">REST</xref>) nor the query format used to
        query the Passive DNS. Neither does this document describe
        "pre-recursor" Passive DNS Systems. Each of these are separate topics
        and deserve their own RFC documents. This document describes the
        current best practices implemented in various Passive DNS server
        implementations. </t>

      <section title="Requirements Language">
        <t>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>
      </section>
    </section>

    <section title="Limitations">
      <t> As Passive DNS servers can include protection mechanisms for their operation, results
        might be different due to those protection measures. These mechanisms filter out DNS answers
        if they fail some criteria. The <xref target="BAILIWICK">bailiwick algorithm</xref> protects
        the Passive DNS Database from cache poisoning attacks.
        Another limitation that clients querying the database need to be aware of is that each query
        simply gets a snapshot-in-time answer at the time of querying. Clients MUST NOT rely on
        existing answers from different Passive DNS database. Nor should they assume that answers
        will be identical across multiple Passive DNS servers. </t>
    </section>

    <section title="Common Output Format">
      <section title="Overview">
        <t>The formatting of the answer follows the <xref target="RFC4627">JSON</xref> format. In
          fact, it is a subset of the full JSON language. Notable differences are the modified
          definition of whitespace ("ws"). The order of the fields is not significant for the same
          resource type. </t>
        <t>The intent of this output format is to be easily parsable by scripts. Each JSON object is
          expressed on a single line to be processed by the client line-by-line. Every
          implementation MUST support the JSON output format.</t>
        <!-- note: it is "parsable" if you want to be really nit-picking. See:
        https://en.wiktionary.org/wiki/parsable -->
        <t><xref target="app-additional">Examples of JSON</xref> output are in the appendix.</t>
      </section>

      <section title="ABNF grammar">
        <!-- "preamble" is deprecated in V3 -->
        <t>Formal grammar as defined in <xref target="RFC2234">ABNF</xref></t>
        <figure>
          <artwork><![CDATA[
answer          = entries
entries         = * ( entry newline )
entry           = ws "{" ws keyvallist ws "}" ws
keyvallist      = [ member *( value-separator member ) ]
member          = field name-separator value
name-separator  = ws %x3A ws            ; : colon
value-separator = ws %x2C ws            ; , comma
field           = field-name | futureField
field-name      = "rrname" | "rrtype" | "rdata" | "time_first" |
                  "time_last" | "count" | "bailiwick" | "sensor_id" |
                  "zone_time_first" | "zone_time_last" | "origin" |
                  "time_first_ms" | "time_last_ms"
futureField     = string
newline         = [ CR ] LF
CR              = %x0D                  ; Carrige return
LF              = %x0A                  ; Line feed or New line
qm              = %x22                  ; " Quotation mark
ws              = *(
                    %x20 |              ; Space
                    %x09                ; Horizontal tab
                    )

					]]></artwork>
        </figure>

        <t>Note that value is defined in <xref target="RFC4627">JSON</xref> and has the same
          specification as there. The same goes for the definition of string. Note the changed
          definition of ws does not include CR or LF as those are NOT allowed in NDJSON, and thus
          the definition here MUST be used for other ABNF defitions in <xref target="RFC4627">JSON</xref>
          .</t>
      </section>

      <section title="Mandatory Fields">
        <t>Implementation MUST support all the mandatory fields.</t>
        <t>Uniqueness property: the tuple (rrname,rrtype,rdata) will always be unique within one
          answer per server. While rrname and rrtype are always individual JSON primitive types
          (strings, numbers, booleans or null), rdata MAY return multiple resource records or a
          single record. When multiple resource records are returned, rdata MUST be a JSON array. In
          the case of a single resource record is returned, rdata MUST be a JSON string or a JSON
          array containing one JSON string. Senders SHOULD send an array for rdata, but receivers
          MUST be able to accept a single-string result for rdata.</t>

        <section title="rrname">
          <t>This field returns the name of the queried resource. Represented as a <xref
              target="RFC4627">JSON</xref> string.</t>
        </section>

        <section title="rrtype">
          <t>This field returns the resource record type as seen by the passive DNS. The key is
            rrtype and the value is in the interpreted record type represented as a <xref
              target="RFC4627">JSON</xref> string. If the value cannot be interpreted, the decimal
            value is returned, following the principle of transparency as described in <xref
              target="RFC3597">RFC 3597</xref>. Then the decimal value is represented as a <xref
              target="RFC4627">JSON</xref> number. The resource record type can be any values as
            described by IANA in the DNS parameters document in the section 'Resource Record (RR)
            TYPEs' (http://www.iana.org/assignments/dns-parameters). Supported textual descriptions
            of rrtypes include: A, AAAA, CNAME, etc. A client MUST be able to understand these
            textual rrtype values represented as a <xref target="RFC4627">JSON</xref> string. In
            addition, a client MUST be able to handle a decimal value (as mentioned above) answer
            represented as a <xref target="RFC4627">JSON</xref> number. </t>
        </section>

        <section title="rdata">
          <t>This field returns the resource records of the queried resource. When multiple resource
            records are returned, rdata MUST be a JSON array containing JSON strings. In the case of
            a single resource record being returned, rdata MUST be a JSON string or a JSON array
            containing one JSON string. Each resource record is represented as a <xref
              target="RFC4627">JSON</xref> string. Each resource record MUST be escaped as defined
            in section 2.6 of <xref target="RFC4627">RFC4627</xref>. Depending on the rrtype, this
            can be an IPv4 or IPv6 address, a domain name (as in the case of CNAMEs), an SPF record,
            etc. A client MUST be able to interpret any value which is legal as the right hand side
            in a DNS master file <xref target="RFC1035">RFC 1035</xref> and <xref target="RFC1034">RFC
            1034</xref>. If the rdata came from an unknown DNS resource records, the server must
            follow the transparency principle as described in <xref target="RFC3597">RFC 3597</xref>
            .</t>
        </section>

        <section title="time_first">
          <t>This field returns the first time that the record / unique tuple (rrname, rrtype,
            rdata) has been seen by the passive DNS. The date is expressed in seconds (decimal)
            since 1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is
            represented as a <xref target="RFC4627">JSON</xref> number.</t>
        </section>

        <section title="time_last">
          <t>This field returns the last time that the unique tuple (rrname, rrtype, rdata) record
            has been seen by the passive DNS. The date is expressed in seconds (decimal) since 1st
            of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is represented
            as a <xref target="RFC4627">JSON</xref> number.</t>
        </section>
      </section>

      <section title="Optional Fields">
        <t>Implementations SHOULD support one or more fields.</t>
        <section title="count">
          <t>Specifies how many authoritative DNS answers were received at the Passive DNS server's
            collectors with exactly the given set of values as answers (i.e. same data in the answer
            set - compare with the uniqueness property in "Mandatory Fields"). The number of
            requests is expressed as a decimal value. This field is represented as a <xref
              target="RFC4627">JSON</xref> number.</t>
        </section>
        <section title="bailiwick">
          <t>The bailiwick is the best estimate of the apex of the zone where this data is
            authoritative. This field is represented as a <xref target="RFC4627">JSON</xref> string.</t>
        </section>
      </section>

      <section title="Additional Fields">
        <t>Implementations MAY support the following fields:</t>
        <section title="sensor_id">
          <t>This field returns the sensor information where the record was seen. It is represented
            as a <xref target="RFC4627">JSON</xref> string.</t>
          <t>If the data originate from sensors or probes which are part of a publicly-known
            gathering or measurement system (e.g. RIPE Atlas), a <xref target="RFC4627">JSON</xref>
            string SHOULD be prefixed.</t>
        </section>

        <section title="zone_time_first">
          <t>This field returns the first time that the unique tuple (rrname, rrtype, rdata) record
            has been seen via master file import. The date is expressed in seconds (decimal) since
            1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is
            represented as a <xref target="RFC4627">JSON</xref> number.</t>
        </section>

        <section title="zone_time_last">
          <t>This field returns the last time that the unique tuple (rrname, rrtype, rdata) record
            has been seen via master file import. The date is expressed in seconds (decimal) since
            1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is
            represented as a <xref target="RFC4627">JSON</xref> number.</t>
        </section>

        <section title="origin">
          <t>Specifies the resource origin of the Passive DNS response. This field is represented as
            a <xref target="RFC3986">Uniform Resource Identifier</xref> (URI) in the form of a <xref
              target="RFC4627">JSON</xref> string. </t>
        </section>

        <section title="time_first_ms">
          <t>Same meaning as the field "time_first", with the only difference, that the resolution
            is in milliseconds since 1st of January 1970 (UTC).
          </t>
        </section>

        <section title="time_last_ms">
          <t>Same meaning as the field "time_last", with the only difference, that the resolution is
            in milliseconds since 1st of January 1970 (UTC).
          </t>
        </section>
      </section>

      <section title="Additional Fields Registry">
        <t>In accordance with <xref target="RFC6648" />, designers of new passive DNS applications
          that would need additional fields can request and register new field name at
          https://github.com/adulau/pdns-qof/wiki/Additional-Fields.</t>
      </section>

      <section title="Additional notes">
        <t>An implementer of a passive DNS server MAY chose to either return time_first and
          time_last OR return zone_time_first and zone_time_last. In pseudocode: (time_first AND
          time_last) OR (zone_time_first AND zone_time_last). In this case, zone_time_{first,last}
          replace the time_{first,last} fields. However, this is not encouraged since it might be
          confusing for parsers who will expect the mandatory fields time_{first,last}. See: <xref
            target="github_issue_17" /></t>
      </section>

      <section title="Suggested MIME Types">
        <t>An implementer of a passive DNS server SHOULD serve a document in this Common Output
          Format with a MIME header of "application/x-ndjson".</t>
      </section>
    </section>


    <!-- This PI places the pagebreak correctly (before the section title) in the text output. -->
    <?rfc needLines="8"?>
    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>Thanks to the Passive DNS developers who contributed to the document.</t>
    </section>
    <!-- Possibly a 'Contributors' section ... -->
    <section anchor="IANA" title="IANA Considerations">
      <t>This memo includes no request to IANA.</t>
    </section>

    <section anchor="Privacy" title="Privacy Considerations">
      <t>Passive DNS servers capture DNS answers from multiple collection points ("sensors") which
        are located on the Internet-facing side of DNS recursors ("post-recursor passive DNS"). In
        this process, they intentionally omit the source IP, source port, destination IP and
        destination port from the captured packets. Since the data is captured "post-recursor", the
        timing information (who queries what) is lost, since the recursor will cache the results.
        Furthermore, since multiple sensors feed into a passive DNS system, the resulting data gets
        mixed together, reducing the likelihood that Passive DNS systems are able to find out much
        about the actual person querying the DNS records. In this sense, passive DNS systems are
        similar to keeping an archive of all previous phone books - if public DNS records can be
        compared to phone numbers - as they often are. Nevertheless, the authors strongly encourage
        Passive DNS implementors to take special care of privacy issues. Finally, the overall
        recommendations in <xref target="RFC6973">RFC6973</xref> should be taken into consideration
        when designing any application which uses Passive DNS data.</t>

      <t>Passive DNS attempts to collect information necessary for security (such as malware protection)
        in as privacy protecting a manner as possible, and is intended to be
        used instead of more invasive methods. It does this by only collecting
      DNS cache-fill answers, and not any information associated with who caused the
    name to be resolved, nor why the name was resolved. Nevertheless, it is possible that
  this may still lead to privacy concerns - for example, if Passive DNS records show that
  a recursive resolver resolved the name the-mary-and-john-smith-family.example.com, it may be
  possible to infer that the Smith family is using that resolver. Operators of Passive DNS
  servers should be aware of this and take appropriate steps to limit access to the data.</t>

  <t>Passive DNS operators are encouraged to read and understand
    <xref target="RFC7258">RFC7258</xref> </t>


      <t>In the scope of the General Data Protection Regulation (GDPR - Directive 95/46/EC),
        operators of Passive DNS server needs to ensure the legal ground and lawfulness of its
        operation.</t>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>In some cases, Passive DNS output might contain confidential information and its access
        should be restricted. When a user is querying multiple Passive DNS and aggregating the data,
        the sensitivity of the data must be considered.</t>
    </section>
  </middle>
  <!--  *****BACK MATTER ***** -->
  <back>
  <references>
      <name>Normative References</name>
      &RFC2119; &RFC1035; &RFC1034; &RFC3912; &RFC4627;
      &RFC3597; &RFC6648; &RFC2234; &RFC6973; &RFC3986;
      &RFC7258;

      <reference anchor="WEIMERPDNS"
        target="http://www.enyo.de/fw/software/dnslogger/first2005-paper.pdf">
        <front>
          <title>Passive DNS Replication</title>
          <author fullname="Florian Weimer" />
          <date year="2005" />
        </front>
      </reference>

      <reference anchor="PDNSCOF" target="https://github.com/D4-project/analyzer-d4-passivedns/">
        <front>
          <title>Passive DNS server interface using the common output format</title>
          <author fullname="D4 Project, Alexandre Dulaunoy" />
          <date year="2019" />
        </front>
      </reference>

      <reference anchor="github_issue_17" target="https://github.com/adulau/pdns-qof/issues/17">
        <front>
          <title>Discussion on the existing implementations of returning either
            zone_time{first,last} OR time_{first,last}</title>
          <author fullname="Paul Vixie, Weizman, April, Kaplan, et.al" />
          <date year="2020" />
        </front>
      </reference>
    </references>

    <references>
      <name>Informative References</name>
      &RFC7871;

      <reference anchor="BAILIWICK"
      target="https://archive.farsightsecurity.com/Passive_DNS/passive_dns_hardening_handout.pdf">
      <front>
        <title>Passive DNS Hardening</title>
        <author fullname="Robert Edmonds" />
        <date year="2010" />
      </front>
    </reference>

      <reference anchor="PDNSCLIENT" target="https://github.com/chrislee35/passivedns-client">
        <front>
          <title>Queries 5 major Passive DNS databases: BFK, CERTEE, DNSParse, ISC, and VirusTotal.</title>
          <author fullname="Chris Lee" />
          <date year="2013" />
        </front>
      </reference>

      <reference anchor="REST"
      target="http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm">
      <front>
        <title>Representational State Transfer (REST)</title>
        <author fullname="Roy Thomas Fielding" />
        <date year="2000" />
      </front>
    </reference>

    <reference anchor="DNSDB" target="https://api.dnsdb.info/">
      <front>
        <title>DNSDB API</title>
        <author fullname="Farsight Security" />
        <date year="2013" />
      </front>
    </reference>

    <reference anchor="PDNSCIRCL" target="https://www.circl.lu/services/passive-dns/">
      <front>
        <title>CIRCL Passive DNS</title>
        <author fullname="CIRCL -Computer Incident Response Center Luxembourg" />
        <date year="2012" />
      </front>
    </reference>

    <reference anchor="DNSDBQ" target="https://github.com/dnsdb/dnsdbq">
      <front>
        <title>DNSDB API Client, C Version</title>
        <author fullname="Paul Vixie" />
        <date year="2018" />
      </front>
    </reference>
    </references>

    <section anchor="app-additional" title="Examples">
      <t>The JSON output are represented on multiple lines for readability but each JSON object
        should be on a single line.</t>
      <t>If you query a passive DNS for the rrname www.ietf.org, the passive dns common output
        format can be:</t>
      <figure>
        <artwork><![CDATA[
{"count": 102, "time_first": 1298412391, "rrtype": "AAAA",
"rrname": "www.ietf.org", "rdata": "2001:1890:1112:1::20",
"time_last": 1302506851}
{"count": 59, "time_first": 1384865833, "rrtype": "A",
"rrname": "www.ietf.org", "rdata": "4.31.198.44",
"time_last": 1389022219}
        ]]></artwork>
      </figure>
      <t>If you query a passive DNS for the rrname ietf.org, the passive dns common output format
        can be:</t>
      <figure>
        <artwork><![CDATA[
{"count": 109877, "time_first": 1298398002, "rrtype": "NS",
"rrname": "ietf.org", "rdata": "ns1.yyz1.afilias-nst.info",
"time_last": 1389095375}
{"count": 4, "time_first": 1298495035, "rrtype": "A",
"rrname": "ietf.org", "rdata": "64.170.98.32",
"time_last": 1298495035}
{"count": 9, "time_first": 1317037550, "rrtype": "AAAA",
"rrname": "ietf.org", "rdata": "2001:1890:123a::1:1e",
"time_last": 1330209752}
        ]]></artwork>
      </figure>
      <t>Please note that the examples imply that a single query returns a single set of JSON
        objects. For example, two queries were made; one query returned a set of two JSON objects
        and the other query returned a set of three JSON objects. This specification requires each
        JSON object individually MUST conform to the common output format, but this specification
        does not require that a query will return a set of JSON objects.</t>
      <t>Please note that in the examples above, any backslashes "\" can be ignored and are an
        artifact of the tools which produced this document.</t>
    </section>
  </back>
</rfc>