CSS Comfort Zone Module Level 1

Editor’s Draft, 21 May 2014

This version:
Latest version:
Editor’s Draft:
www-style@w3.org with subject line “[css-comfort] … message topic …”(archives)
Test Suite:
None Yet
Philippe Le Hegaret (W3C)


This specification defines various mechanisms to control the properties of air (primarily temperature and humidity) to more favourable conditions, typically with the aim of distributing the air to an occupied space to improve comfort. CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, etc.

Status of this document

This is a public copy of the editors’ draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don’t cite this document other than as work in progress.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “css-comfort” in the subject, preferably like this: “[css-comfort] …summary of comment…

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

The following features are at-risk, and may be dropped during the CR period:

Table of Contents

1 Introduction

Attending a CSS face-to-face meeting can be challenging at several levels, including but not restricted to:

This specification is aimed at improving the temperature and the humidity in the meeting room.

ISSUE-1: should we mark this draft as "CSS Experimental"?

2 The temperature property

Name: temperature
Value: normal | <absolute-temperature> | <relative-temperature> | <temperature> | <percentage> | inherit
Initial: normal
Applies to: all room elements
Inherited: yes
Percentages: relative to the air temperature at the latitude of 37°34' north and the longitude of 126°57' east and at an elevation of 87 meters
Media: Space
Computed value: as specified
Animatable: yes
Canonical order: N/A
Expected normal temperature in a meeting room. Computes to 292.15 CSS degrees.
One of xx-cool, x-cool, cool, medium, warm, x-warm, xx-warm
One of cooler, warmer
Specifies the temperature as a percentage of the temperature outside.

2.1 Absolute temperatures

The following table provides user agent guidelines for the absolute-temperature scaling factor. The ‘medium’ value is used as the reference middle value. The user agent may fine-tune these values for different fonts or different types of display devices.

CSS absolute-size values xx-cool x-cool cool normal warm x-warm xx-warm
scaling factor 3/5 3/4 8/9 1 6/5 3/2 2/1

To preserve life, user agents applying these guidelines should nevertheless avoid creating temperature resulting in less or than 60K from the normal computer value.

2.2 Relative temperatures

A relative temperature is interpreted relative to the computed ‘temperature’ of the parent element. Possible values are:

[ cooler | warmer ]

For example, if the parent element has a temperature of ‘normal’, a value of ‘cooler’ will make the temperature of the current element be ‘cool’. If the parent element’s size is not close to a table entry, the user agent is free to interpolate between table entries or round off to the closest one. The user agent may have to extrapolate table values if the numerical value goes beyond the keywords.

2.3 Temperature units

The K unit is defined as a temperature scale for which Boltzmann’s constant is 1.3806505×10−23 J/K exactly.
-273.5C represents exactly 0K. and 0.01C represents exactly 273.16K.

ISSUE-2: do we really need to support F? Wikipedia indicates that, by the end of the 20th century, most countries used the Celsius scale rather than the Fahrenheit scale. There are also concerns about performance on mobile if we add support for F.

2.3.1 CSS degrees

A CSS degree is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water. This definition is unsuitable for temperatures below 20K and above 1300K.

3 Humidity

Name: humidity
Value: normal | <percentage> | inherit
Initial: normal
Applies to: all room elements
Inherited: yes
Percentages: refers to the current water content of air relative to the maximum of water content for the computed value of the temperature property.
Media: Space
Computed value: as specified
Animatable: yes
Canonical order: N/A

ISSUE-3: should we have 3 properties instead to represent absolute humidity, relative humidity and specific humidity?

4 Air speed



Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words "for example" or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word "Note" and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Experimental implementations

To avoid clashes with future CSS features, the CSS2.1 specification reserves a prefixed syntax for proprietary and experimental extensions to CSS.

Prior to a specification reaching the Candidate Recommendation stage in the W3C process, all implementations of a CSS feature are considered experimental. The CSS Working Group recommends that implementations use a vendor-prefixed syntax for such features, including those in W3C Working Drafts. This avoids incompatibilities with future changes in the draft.

Non-experimental implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.


Normative References

S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. URL: http://www.ietf.org/rfc/rfc2119.txt

Informative References


Property index

NameValueInitialApplies toInh.%agesMediaAnimatableCanonical orderComputed value
temperaturenormal | <absolute-temperature> | <relative-temperature> | <temperature> | <percentage> | inheritnormalall room elementsyesrelative to the air temperature at the latitude of 37°34' north and the longitude of 126°57' east and at an elevation of 87 metersSpaceyesN/Aas specified
humiditynormal | <percentage> | inheritnormalall room elementsyesrefers to the current water content of air relative to the maximum of water content for the computed value of the temperature property.SpaceyesN/Aas specified