Specification

Tree preservation order

Abstract

This specification defines the contents and format of data which a relevant planning authority or other party may use to provide information about one or more Tree preservation orders.

Status of this specification

Piloting

Warning It is inappropriate to cite this draft document as other than a work in progress.

This document sets out the requirements for providing data in conformance to the specification which is currently under development. Providing data to this draft specification is at present optional, though encouraged.

This is a draft specification, following the standards for planning data process [design-process]. The contents of this specification are currently under development, and liable to change based on feedback.

This document places no obligations on any party to provide data in conformance to this specification.

A future version of this specification may be formally published on GOV.UK, and cited as one of a number of official data standards for the provision of planning data under the Levelling-up and Regeneration Act 2023 [LURA] or other legislation.

This technical specification is accompanied by guidance, examples and other tools which provide feedback to organisations creating data to this specification.

Comments and feedback on this specification may be provided on the GitHub discussion or sent to digitalland@communities.gov.uk.

Version: 1.3.1 — published 2025-11-08

See versions — See changelog

Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

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

Datasets and fields

This section is non-normative

An index of the datasets and fields defined by this specification.

Tree preservation order
Field Requirement Datatype
reference reference
name string
documentation-url URL
document-url URL
made-date datetime
confirmed-date datetime
notes text
organisation reference
entry-date datetime
start-date datetime
end-date datetime
Tree preservation zone
Field Requirement Datatype
reference reference
name string
tree-preservation-order string
tree-preservation-zone-type string
geometry geometry
point point
notes text
organisation reference
entry-date datetime
start-date datetime
end-date datetime
Tree
Field Requirement Datatype
reference reference
name string
tree-preservation-order string
uprn string
address-text string
point point
geometry geometry
notes text
organisation reference
felled-date datetime
entry-date datetime
start-date datetime
end-date datetime

Dataset relationships

This section is non-normative

The following diagram illustrates the datasets specified by this document, and how data in a dataset entry may reference, or be referenced by an entry in another dataset.

Dataset details

Tree preservation order

The Tree preservation order dataset contains .

The Tree preservation order dataset contain at least one entry for each Tree preservation order for which the data provider is the responsible authority.

Reference

Enter reference to help people find and link to the data. If you don’t have a reference for this item, you will need to create one that is:

  • unique within your data
  • persistent — it doesn’t change when the data is updated

A good reference is something you already use. Where these aren't unique, you make them unique by appending the year, or even the full date. Great references are short, easy to read, to pronounce and remember.

Each Tree preservation order entry MAY contain a reference field value.

The Tree preservation order reference field MUST be a reference value.

The <a href="#reference">reference</a> for the tree preservation order.

Name

Each Tree preservation order entry MAY contain a name field value.

The Tree preservation order name field MUST be a string value.

The name of the tree preservation order.

Documentation URL

Each Tree preservation order entry MAY contain a documentation-url field value.

The Tree preservation order documentation-url field MUST be a URL value.

The URL of the web page where you can find information about the tree preservation order.

Document URL

A url to a document.

Each Tree preservation order entry MAY contain a document-url field value.

The Tree preservation order document-url field MUST be a URL value.

The URL of the tree preservation order document. If a TPO is revoked you can blank out this field..

Made date

The date a tree preservation order was "made". From this date the included tree(s), from a planning perspective, are considered to be covered by a tree preservation order..

Each Tree preservation order entry MAY contain a made-date field value.

The Tree preservation order made-date field MUST be a datetime value.

The date the tree preservation order was "made".

Confirmed date

The date a tree preservation order is confirmed and becomes a fully fledged tree preservation order..

Each Tree preservation order entry MAY contain a confirmed-date field value.

The Tree preservation order confirmed-date field MUST be a datetime value.

The date the tree preservation order was "confirmed".

Notes

Notes and commentary about how this data was made or may be interpreted.

Enter any notes or commentary which helps you or others understand how this data was made, or how it may be interpreted.

Each Tree preservation order entry MAY contain a notes field value.

The Tree preservation order notes field MUST be a text value.

Optional notes.

Organisation

Department, agency, body, company, group, or association of people.

Enter a CURIE value for the organisation from this list.

Each Tree preservation order entry MAY contain an organisation field value.

The Tree preservation order organisation field MUST be a reference value.

The organisation responsible for this tree preservation order.

Entry date

Entry date of the data.

Enter the date this data was created or modified.

Each Tree preservation order entry MAY contain an entry-date field value.

The Tree preservation order entry-date field MUST be a datetime value.

The <a href="#date">date</a> this entry was created or amended.

Start date

Date the entity became active or in force.

Each Tree preservation order entry MAY contain a start-date field value.

The Tree preservation order start-date field MUST be a datetime value.

The <a href="#date">date</a> the tree preservation order came into force.

End date

Date from which the entity is not longer active or in force.

Each Tree preservation order entry MAY contain an end-date field value.

The Tree preservation order end-date field MUST be a datetime value.

The <a href="#date">date</a> the tree preservation order was revoked. Leave blank if the TPO is still active.

Tree preservation zone

The Tree preservation zone dataset contains An area covered by a tree preservation order.

The Tree preservation zone dataset contain at least one entry for each Tree preservation zone for which the data provider is the responsible authority.

Reference

Enter reference to help people find and link to the data. If you don’t have a reference for this item, you will need to create one that is:

  • unique within your data
  • persistent — it doesn’t change when the data is updated

A good reference is something you already use. Where these aren't unique, you make them unique by appending the year, or even the full date. Great references are short, easy to read, to pronounce and remember.

Each Tree preservation zone entry MAY contain a reference field value.

The Tree preservation zone reference field MUST be a reference value.

The <a href="#reference">reference</a> for the tree preservation zone.

Name

Each Tree preservation zone entry MAY contain a name field value.

The Tree preservation zone name field MUST be a string value.

The name of the tree preservation zone.

Tree preservation order

Each Tree preservation zone entry MAY contain a tree-preservation-order field value.

The Tree preservation zone tree-preservation-order field MUST be a string value.

The <a href="#reference">reference</a> for the tree preservation order.

Tree preservation zone type

A category of tree preservation zone.

Each Tree preservation zone entry MAY contain a tree-preservation-zone-type field value.

The Tree preservation zone tree-preservation-zone-type field MUST be a string value.

Each Tree preservation zone entry MAY contain a reference value from the tree-preservation-zone-type dataset.

The type of zone, for example area, group or woodland.

Geometry

A polygon or multipolygon boundary.

The boundary may be a single polygon, or a multipolygon value. All points should be in the WGS84 coordinate reference system. You may provide data containing points in another coordinate reference system, such as British National Grid, but they will need to be transformed into WGS84 by software such as the Planning Data platform and this transformation may lead to a small loss of accuracy. Geometry data provided in a CSV file should use the well-known text (WKT) representation for the field. If you're providing geometry in a GeoJSON, GML, Geopackage or KML, use the appropriate representation for the file format.

Each Tree preservation zone entry MAY contain a geometry field value.

The Tree preservation zone geometry field MUST be a geometry value.

The boundary of the area covered by the tree preservation zone in WKT format.

Point

Each Tree preservation zone entry MAY contain a point field value.

The Tree preservation zone point field MUST be a point value.

The centre of the tree preservation zone if you cannot provide the full geometry.

Notes

Notes and commentary about how this data was made or may be interpreted.

Enter any notes or commentary which helps you or others understand how this data was made, or how it may be interpreted.

Each Tree preservation zone entry MAY contain a notes field value.

The Tree preservation zone notes field MUST be a text value.

Optional notes.

Organisation

Department, agency, body, company, group, or association of people.

Enter a CURIE value for the organisation from this list.

Each Tree preservation zone entry MAY contain an organisation field value.

The Tree preservation zone organisation field MUST be a reference value.

The organisation responsible for this tree preservation order.

Entry date

Entry date of the data.

Enter the date this data was created or modified.

Each Tree preservation zone entry MAY contain an entry-date field value.

The Tree preservation zone entry-date field MUST be a datetime value.

The <a href="#date">date</a> this entry was created or amended.

Start date

Date the entity became active or in force.

Each Tree preservation zone entry MAY contain a start-date field value.

The Tree preservation zone start-date field MUST be a datetime value.

The <a href="#date">date</a> the tree preservation zone came into force.

End date

Date from which the entity is not longer active or in force.

Each Tree preservation zone entry MAY contain an end-date field value.

The Tree preservation zone end-date field MUST be a datetime value.

The <a href="#date">date</a> the tree preservation zone ended or leave blank if the zone is still active.

Tree

The Tree dataset contains An individual tree.

The Tree dataset contain at least one entry for each Tree for which the data provider is the responsible authority.

Reference

Enter reference to help people find and link to the data. If you don’t have a reference for this item, you will need to create one that is:

  • unique within your data
  • persistent — it doesn’t change when the data is updated

A good reference is something you already use. Where these aren't unique, you make them unique by appending the year, or even the full date. Great references are short, easy to read, to pronounce and remember.

Each Tree entry MAY contain a reference field value.

The Tree reference field MUST be a reference value.

The number or reference for the tree which appears in the preservation order.

Name

Each Tree entry MAY contain a name field value.

The Tree name field MUST be a string value.

The name of the tree.

Tree preservation order

Each Tree entry MAY contain a tree-preservation-order field value.

The Tree tree-preservation-order field MUST be a string value.

The <a href="#reference">reference</a> for the tree preservation order.

UPRN

Each Tree entry MAY contain an uprn field value.

The Tree uprn field MUST be a string value.

Unique property reference number if the tree is located on an addressable property.

Address text

Address as a single line of text, separated by commas.

Each Tree entry MAY contain an address-text field value.

The Tree address-text field MUST be a string value.

The address of the property.

Point

Each Tree entry MAY contain a point field value.

The Tree point field MUST be a point value.

The centre of the tree area if you cannot provide the full geometry.

Geometry

A polygon or multipolygon boundary.

The boundary may be a single polygon, or a multipolygon value. All points should be in the WGS84 coordinate reference system. You may provide data containing points in another coordinate reference system, such as British National Grid, but they will need to be transformed into WGS84 by software such as the Planning Data platform and this transformation may lead to a small loss of accuracy. Geometry data provided in a CSV file should use the well-known text (WKT) representation for the field. If you're providing geometry in a GeoJSON, GML, Geopackage or KML, use the appropriate representation for the file format.

Each Tree entry MAY contain a geometry field value.

The Tree geometry field MUST be a geometry value.

The boundary of the area covered by the tree in WKT format.

Notes

Notes and commentary about how this data was made or may be interpreted.

Enter any notes or commentary which helps you or others understand how this data was made, or how it may be interpreted.

Each Tree entry MAY contain a notes field value.

The Tree notes field MUST be a text value.

Optional notes.

Organisation

Department, agency, body, company, group, or association of people.

Enter a CURIE value for the organisation from this list.

Each Tree entry MAY contain an organisation field value.

The Tree organisation field MUST be a reference value.

The organisation responsible for this tree.

Felled date

The date a tree was felled.

Each Tree entry MAY contain a felled-date field value.

The Tree felled-date field MUST be a datetime value.

The date the tree was felled.

Entry date

Entry date of the data.

Enter the date this data was created or modified.

Each Tree entry MAY contain an entry-date field value.

The Tree entry-date field MUST be a datetime value.

The <a href="#date">date</a> this entry was created or amended.

Start date

Date the entity became active or in force.

Each Tree entry MAY contain a start-date field value.

The Tree start-date field MUST be a datetime value.

The <a href="#date">date</a> from which the tree preservation order affects the tree.

End date

Date from which the entity is not longer active or in force.

Each Tree entry MAY contain an end-date field value.

The Tree end-date field MUST be a datetime value.

The <a href="#date">date</a> the tree preservation order no longer affects the tree, or leave blank if the tree is still under the order. Use the felled-date if the tree has been felled..

Source documentation

The source documentation is a web page where the user should go to confirm the validity of information provided in the data.

The source documentation SHOULD be a web page accessible as [HTML] from a public URL.

Finding the information on the organisation's official website helps users check the information in the data. It increases the trust the user may place in the origin of the data, and that it is more likely to be sustained.

The source documentation SHOULD be on the offical website for the organisation.

A Local Authority or other public body should put the documentation page under their .gov.uk domain.

The source documentation MAY either contain the endpoint documentation, or link to one or more separate endpoint documentation pages.

Endpoint documentation

The endpoint documentation is a web page where a user can find a link to where they can download the data (the endpoint), along with other information relevant to a data user, such as the date the data was last updated. Every endpoint needs to be findable via a link on the source documentation page, and the endpoint documentation can be on the source page, on a separate documentation point for each endpoint, or a combination thereof.

The documentation for an endpoint SHOULD be accessible as [HTML] from a public URL.

The endpoint documentation URL SHOULD have the same URL as the endpoint documentation page.

The endpoint documentation URL MAY have the same URL as the source documentation page.

The endpoint documentation include a hyperlink to one or more endpoints for tree preservation order data.

The endpoint documentation include a hyperlink to one or more endpoints for tree preservation zone data.

The endpoint documentation include a hyperlink to one or more endpoints for tree data.

The endpoint documentation page SHOULD include a clear licence for reusing the data.

The data SHOULD be published as [crown-copyright] under [OGL3].

This data is © Crown copyright and available under the Open Government Licence v3.0.

The endpoint documentation page SHOULD include any further attribution a user of the data needs to provide if they copy, publish, distribute or otherwise retransmit the data.

Datatypes

Reference

The reference MAY be used to refer to the entity by other data.

A reference value MUST be either a [CURIE] or the reference part of a [CURIE] identifier.

A reference SHOULD be persistent. A reference SHOULD be used by the data provider to identify the same entity in the future.

A reference SHOULD NOT be used to refer to a different entity in the future.

Where a reference has been used to refer to two different entities, add a year or other text to disambiguate the references, for example use 'CA01' and 'CA01/2022' rather than just 'CA01' for two different conservation areas.

A reference SHOULD be short and meaningful to a user.

A good reference is short, meaningful and easily read out loud by a user. It should be something you already use, such as the reference number sent in letters, asked for in forms, a section reference in documents, the significant part of the URL for an entity (its "furl" or "slug"), or a fragment identifier (anchor) in your source documentation web page.

Datetime

Dates MUST conform to [ISO8601] following the [Open Standards for government guidance [formatting-dates-and-times-in-data].

A date value SHOULD be blank if it is unknown.

The date MAY just contain the year 'YYYY' if only the year is known, or 'YYYY-MM' if only the year and month is known.

Geometry

A geometry field MAY be eiher a single POLYGON or MULTIPOLYGON value.

When using Comma Separated Value (CSV), the geometry SHOULD be encoded as Well Known Text [WKT].

All points SHOULD be either in the [WGS84] (EPSG::4326) or [ETRS89] (EPSG::4258) coordinate reference system following the [Open Standards for government] guidance [exchange-of-location-point].

Boundaries provided by this dataset are intended to be used as an index. Positions calculated by the WGS84 and ETRS89 systems can currently deviate by half a metre for points within England. Survey data should be used where more precision is needed.

Coordinate values SHOULD be 6 or fewer decimal places.

Integer

A value in the integer values MUST conform to the integer datatype as defined by [tabular-metadata].

Text

All text values SHOULD be compatible with [govspeak-markdown].

All text values MUST be encoded in UTF-8 [RFC3629] following the [Open Standards for government] guidance [encoding-characters].

URL

All URL values MUST conform to [RFC3986].

For the purposes of this specification, the terms URL, URI and IRI are synonymous as set out in [URL-interoperability]

String

All string values MUST be encoded in UTF-8 [RFC3629] following the [Open Standards for government] guidance [encoding-characters].

Historical data

Removing historical data can reduce the trust a user places in the quality of the data. There are also many uses for historical documents, data and material information in planning, such as when developing an older property, processing an appeal, and monitoring the delivery of housing on older brownfield land, and when collecting evidence for plan-making.

Entries SHOULD NOT be changed or removed from the data except to correct a mistake, or for the purposes of redacting personal or otherwise sensitive information.

An entity SHOULD be updated by adding another entry to the data with the same reference and a newer entry-date.

Entries SHOULD be ordered within a dataset by the entry-date value, with older entries appearing before later entries.

The end-date field SHOULD be used to indicate when an entity is no longer applicable.

Data file formats

Data MUST be provided in at least one of the following file formats:

The preferred format for geospatial data is GeoJSON.

Tabular data SHOULD be provided as (CSV) [RFC4180] following the [Open Standards for government] guidance [tabular-data-standard].

Field names

The case and punctuation used in field names is insignificant, meaning 'StartDate', 'Start Date' 'START_DATE' and 'start.date', are all valid ways of naming the 'start-date' field.

A field name SHOULD be treated as being case insensitive.

A non-alphanumeric character in a field name SHOULD be ignored.

Evolution

This specification is expected to evolve through compatible evolution:
  1. Data may contain additional fields in the future. Processors must ignore any fields they aren't expecting.
  2. Fields in this specification will be deprecated in a future version, rather than being removed.
  3. Future versions of this specification MUST NOT significantly change the meaning of any of the fields in this version of the specification.

A sending processor conforming to this specification MAY include unspecified fields and values.

A receiving processor conforming to this specification MUST ignore any unspecified fields and their values.

Extensibility

The approach for evolution enables processors to extend the specification by including fields and data for their own purposes.

A processor SHOULD NOT add fields likely to be used in a future version of this specification for different purposes.

Endpoint

The endpoint is the URL for where data in a format defined by this specification may be downloaded. The Other patterns for collecting data are under consideration, including feeds for large datasets which change frequently.

Your data must be on a URL the public can access. We collect the latest data from there every day. We call this the ‘endpoint URL’.

Endpoints typically fall into 1 of the following 2 categories:

  • a file hosted on your web server — these will usually be URLs which end in something like .json or .csv
  • an API — these are usually hosted by your GIS (Geographic Information System) software or open data platform

Whenever your data changes, update it in the endpoint URL. Your endpoint URL should remain the same, do not change it when you make updates.

The endpoint MUST serve data conforming to this specification.

The endpoint MUST be accessible via HTTPS.

The data MUST be publicly accessible without authentication or authorisation.

Security and privacy considerations

There is a risk of people's names or other personally identifiable information appearing in the data, in particular notes, description and other text fields. It is the responsibility of the data provider to review and redact such information before publication.

The [OGL3] licence does not cover personal data in the Information.

The data MUST NOT contain any personal or sensitive information, unless explicitly required by this specification, or legislation.

Colophon

This document is © Crown Copyright and available under the Open Government Licence version 3 licence.

References

Normative references

[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. IETF Best Current Practice. https://tools.ietf.org/html/rfc2119
[RFC8174]
Ambiguity of Uppercase vs Lowercase in [RFC2119] Key Words. IETF Best Current Practice. https://datatracker.ietf.org/doc/html/rfc8174
[RFC3629]
UTF-8, a transformation format of ISO 10646. IETF Internet Standard. https://datatracker.ietf.org/doc/html/rfc3629
[RFC4180]
Common Format and MIME Type for Comma-Separated Values (CSV) Files. IETF Informational. https://datatracker.ietf.org/doc/html/rfc4180
[RFC7946]
The GeoJSON Format. Proposed Standard. https://datatracker.ietf.org/doc/html/rfc7946
[RFC3339]
Date and Time on the Internet: Timestamps. IETF Proposed Standard. https://datatracker.ietf.org/doc/html/rfc3339
[RFC3986]
IETF Standard. Uniform Resource Identifier (URI): Generic Syntax. https://datatracker.ietf.org/doc/html/rfc3986
[URI-Fragment]
Section 3.5 of [RFC3986] Fragment Identifier of a URI https://datatracker.ietf.org/doc/html/rfc3986#section-3.5
[tabular-metadata]
Metadata Vocabulary for Tabular Data. W3C Recommendation. https://www.w3.org/TR/2015/REC-tabular-metadata-20151217/
[tabular-data-model]
Model for Tabular Data and Metadata on the Web. W3C Recommendation. https://www.w3.org/TR/2015/REC-tabular-data-model-20151217
[CURIE]
CURIE Syntax 1.0 A syntax for expressing Compact URIs. W3C Working Group Note. https://www.w3.org/TR/2010/NOTE-curie-20101216/
[GML]
Geography Markup Language (GML). Open Geospatial Consortium standard (ISO 19136-1:2020). https://www.ogc.org/standards/gml
[KML]
OGC KML 2.3. Open Geospatial Consortium standard (12-007r2). http://www.opengis.net/doc/IS/kml/2.3
[Geopackage]
OGC Geopackage 1,4 Open Geospatial Consortium standard (12-128r19). http://www.opengis.net/doc/IS/geopackage/1.4
[WGS84]
National Imagery and Mapping Agency, "Department of Defense World Geodetic System 1984: Its Definition and Relationships with Local Geodetic Systems", Third Edition, 1984. The code for this standard in the European Petroleum Survey Group (EPSG) Registry is [EPSG::4326]. https://nsgreg.nga.mil/doc/view?i=4085
[ETRS89]
The European Terrestrial Reference System 89 (ETRS89) The code for this standard in the European Petroleum Survey Group (EPSG) Registry is [EPSG::4258]. http://etrs89.ensg.ign.fr/
[WKT]
OGC Well-known text (WKT) as defined by ISO/IEC 13249-3:2016. https://www.iso.org/standard/60343.html
[ISO8601]
Data elements and interchange formats – Information interchange – Representation of dates and times", ISO 8601:1988(E), International Organization for Standardization, June, 1988.
[OGL3]
Open Government Licence for public sector information. Version 3. https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/
[crown-copyright]
Crown copyright. Section 163 of the Copyright, Designs and Patents Act 1988 as works made by officers or servants of the Crown in the course of their duties. https://www.nationalarchives.gov.uk/information-management/re-using-public-sector-information/uk-government-licensing-framework/crown-copyright/

Informative references

[LURA]
Levelling-up and Regeneration Act. Originated in the House of Commons, Session 2022-23. https://www.legislation.gov.uk/ukpga/2023/55/enacted
[process]
Ministry for Housing, Communities & Local Government planning data standards design process (service under development). https://design.planning.data.gov.uk
[GSS]
Office for National Statistics, Geography Coding and Naming Policy for Official Statistics Version 2.0, July 2025 https://geoportal.statistics.gov.uk/documents/5a050dcaac8049dc9dc0aa7de0943378/about
[govspeak-markdown]
How to publish on GOV.UK: Govspeak Markdown. https://www.gov.uk/guidance/how-to-publish-on-gov-uk/markdown
[open-standards-for-government]
Government Digital Service and Central Digital and Data Office. Open standards for government
[encoding-characters]
Encoding characters Open Standards for Government. https://www.gov.uk/government/publications/open-standards-for-government/cross-platform-character-encoding-profile
[persistent-resolvable-identifiers]
Persistent resolvable identifiers. Open Standards for Government. https://www.gov.uk/government/publications/open-standards-for-government/persistent-resolvable-identifiers
[formatting-dates-and-times-in-data]
Formatting dates and times in data. Open Standards for Government. https://www.gov.uk/government/publications/open-standards-for-government/date-times-and-time-stamps-standard
[publishing-government-documents]
Publishing government documents. Open Standards for Government. https://www.gov.uk/government/publications/open-standards-for-government/viewing-government-documents
[exchange-of-location-point]
Exchange of location point. Open Standards for Government. https://www.gov.uk/government/publications/open-standards-for-government/exchange-of-location-point
[tabular-data-standard]
Tabular data standard. Open Standards for Government. https://www.gov.uk/government/publications/recommended-open-standards-for-government/tabular-data-standard
[using-csv]
Using CSV file format. Central Digital and Data Office guidance. https://www.gov.uk/guidance/using-csv-file-format
[csv-on-the-web]
CSV on the Web: A Primer. W3C Working Group Note. https://www.w3.org/TR/tabular-data-primer/
[EPSG::4326]
World Geodetic System 1984 [WGS84] EPSG Geodetic Parameter Dataset. https://epsg.io/4326
[EPSG::4258]
The European Terrestrial Reference System 89 [ETRS89] EPSG Geodetic Parameter Dataset. https://epsg.io/4326
[GDAL]
GDAL. Open Source Geospatial Foundation. https://gdal.org/
[TAB]
MapInfo TAB format. https://en.wikipedia.org/wiki/MapInfo_TAB_format
[Shapefile]
ESRI Shapefile format. https://en.wikipedia.org/wiki/Shapefile
[ZIP]
ZIP format. https://en.wikipedia.org/wiki/ZIP_(file_format)
[HTML]
WHATWG HTML. Living Standard. https://html.spec.whatwg.org/
[URL-interoperability]
WHATWG URL. Living Standard. Interoperability of URL with URI and IRI values. https://url.spec.whatwg.org/

Previous versions

These specifications are living documents. When we make material changes to the data structure we update the version number.

Previous versions of the tree-preservation-order specification are: