CSS Print Profile

Editor’s Draft,

This version:
https://dev.w3.org/csswg/css-print/
Latest published version:
http://www.w3.org/TR/css-print/
Previous Versions:
https://www.w3.org/TR/2013/NOTE-css-print-20130314/
Editors:
Elika J. Etemad
Melinda Grant (Hewlett-Packard Company)
Issue Tracking:
GitHub Issues

Abstract

This specification defines a subset of Cascading Style Sheets Level 2, revision 1 [CSS21] and CSS Paged Media Level 3 [CSS3PAGE] for printing to low-cost devices. It is designed for printing in situations where it is not feasible or desirable to install a printer-specific driver, and for situations were some variability in the output is acceptable.

This profile is designed to work in conjunction with XHTML-Print [XHTML-PRINT] and defines a minimum level of conformance as well as an extension set that provides stronger layout control for the printing of mixed text and images, tables and image collections.

This profile is obsolete. Please see the latest CSS Snapshot for the specifications that make up CSS.

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.

GitHub Issues are preferred for discussion of this specification. When filing an issue, please put the text “css-mobile” in the title, preferably like this: “[css-mobile] …summary of comment…”. All issues and comments are archived, and there is also a historical archive.

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.

This document is governed by the 1 September 2015 W3C Process Document.

Relative to the previous Candidate Recommendation, this version adds two new features (object-fit and object-position), synchronizes this profile with changes to XHTML-Print, removes redundancies with CSS Paged Media Level 3 and makes miscellaneous clarifications and editorial improvements.

Relative to the previous Working Draft, this version updates the names and behavior of object-fit and object-position to match the Candidate Recommendation of CSS Images and Replaced Content Level 3 (and adds a mapping allowance), and updates references to CSS Paged Media Level 3 and CSS 2.1.

At this time, the CSS Working Group does not envisage further work on this specification and does not plan to propose it as a W3C Recommendation.

CSS Print Profile

1. 1. Overview

All sections of this document are normative unless noted as informative.

This document specifies a profile of the Cascading Style Sheets, level 2, revision 1 (CSS 2.1) specification [CSS21] along with the CSS Paged Media Level 3 [CSS3PAGE] and CSS Images Level 3 [CSS3-IMAGES]

CSS 2.1 specifies how developers can author style sheets for presenting documents across multiple devices and media types. While this is very important, it is also important that authors have an understanding of what features are supported on these different devices. Likewise, it is important that similar devices operate in a similar manner. Otherwise, authors could need to develop style sheets for each version of each device -- raising the cost of content development and decreasing interoperability.

The CSS Print Profile specifies a conformance profile for printing in environments where it is not feasible or desirable to use a printer-specific driver. An example of such an environment is printing to low-cost printers from mobile phones.  The profile identifies a minimum set of properties, values, selectors, and cascading rules to support these use scenarios. This profile was designed in conjunction with XHTML-Print [XHTML-PRINT]) for low cost printers that may not have a full-page buffer and that generally print from top-to-bottom.

This profile also contains an enhanced layout extension set which supports more exacting page layouts and orientations. These features provide sufficient richness to print, for example, photo album pages from a digital still camera or print-targeted television content.

Conformance to this profile means that a user agent supports, at a minimum, the features defined in this specification. This subject is addressed in Section 2, Conformance below.

2. 2. Conformance

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 RFC 2119 (see [RFC2119]). However, for readability, these words do not appear in all uppercase letters in this specification.

The primary role of a profile is to define a subset of features that provides a minimal guarantee of interoperability. In the case of the CSS Print Profile, this guarantee is that a conforming user agent will support the features defined in this specification following the CSS 2.1 conformance clause ([CSS21] Section 3.2), recast and summarized below:

  1. A CSS Print Profile conforming user agent (PP-UA or more simply "printer") SHALL support the all and print CSS 2.1 media types. A printer MAY support other CSS 2.1 media types, as well.
  2. For each source document, a printer SHALL attempt to retrieve all associated style sheets that are appropriate for the supported media types. A failure to retrieve a style sheet due to problems such as a loss of network connection SHOULD NOT stop the printer from processing the document.
  3. A printer SHALL parse the style sheets according to this specification. In particular, the printer SHALL recognize all CSS Print Profile at-rules, blocks, declarations, and selectors. If a printer encounters a property that applies for a supported media type, the printer SHALL parse the value according to the property definition. This means that the printer SHALL accept all valid values and MAY ignore declarations with invalid values. A printer SHALL ignore rules that apply to unsupported media types.
  4. For each element in a document tree, the printer SHALL assign a value for every applicable property according to the property’s definition and the rules of cascading and inheritance.
  5. If the source document comes with alternate style sheets (such as with the "alternate" keyword in HTML 4.01 [HTML401]), the printer MAY ignore the style sheet or treat it in some implementation dependent manner.

As with CSS 2.1, there are qualifications to this conformance clause:

  1. Values MAY be approximated when REQUIRED by the printer.
  2. The inability of a printer to implement part of this specification due to the limitations of a particular device (e.g., a printer cannot render colors on a monochrome page) SHALL NOT imply non-conformance.

It is RECOMMENDED that authors use this conformance profile to take advantage of forward compatibility. Authors MAY use style properties with an understanding that the cascading rules are processed correctly and that unknown properties and values are ignored. For example:

  body {
    background-position: center center;
    background-position: 45% 55%; 
  }
 

A printer that can accept percentage values for the background-position property will process the first background-position declaration and then replace that value with the second background-position declaration. A printer that cannot accept percentage values will process the first background-position declaration and ignore the second background-position declaration.

2.1. 2.1. Enhanced Layout Extension Conformance

Some print applications require a more exacting page layout than is available from a minimally conforming printer (e.g., photo album pages or pages from a digital TV). The Enhanced Layout Extension increases the number of properties that a conforming printer MUST support and thereby the requirements of its memory and performance capabilities. These added CSS constructs are indicated with a "MUST" or an increased range of values, in the CSS Print-Enhanced columns below.

Printers supporting the Enhanced Layout Extension MAY also support an OPTIONAL, discoverable (via some means outside the scope of this document) Enhanced Layout Extension indicator.

3. 3. Selectors

In CSS 2.1, pattern matching rules determine which style rules apply to elements in the document tree [CSS21].

Consideration is given to low-cost printers that might not be able to store all the attributes of each element, but only keep the few that are necessary. Therefore, only Enhanced Layout Extension conforming printers MUST support attribute selectors.

The following table summarizes CSS Print Profile selector syntax. In addition to the selectors marked "MUST" in the CSS Print or CSS Print-Enhanced columns, the CSS Print Profile includes the CSS 2.1 grouping mechanism (See [CSS21] Section 5.2.1).

Pattern Meaning Selector type CSS Print CSS Print-Enhanced
* Matches any element Universal selector MUST MUST
E Matches any E element (i.e., any element of type E) Type selectors MUST MUST
E F Matches any F element that is a descendant of an E element Descendant selectors MUST MUST
E > F Matches any F element that is a child of an element E Child selectors MUST MUST
E[foo] Matches any E element with the "foo" attribute set (whatever the value). Attribute selectors MAY MUST
E[foo="warning"] Matches any E element whose "foo" attribute value is exactly equal to "warning". Attribute selectors MAY MUST
E[foo~="warning"] Matches any E element whose "foo" attribute value is a list of space-separated values, one of which is exactly equal to "warning". Attribute selectors MAY MUST
E.classid The same as E[class~=classid] Class selectors MUST MUST
E#myid Matches any E element id equal to "myid". ID selectors MUST MUST
@page :first Specifies style for the first page of a document Page pseudo-classes MUST MUST

3.1. 3.1 At-rules

The following table summarizes CSS Print Profile at-rule syntax.

at-rule Function CSS Print CSS Print-Enhanced
@import Imports an external style sheet. MAY MUST
@charset Defines character set for the style sheet. MUST MUST
@media Groups a set of style rules to apply only to one or more particular media. MUST MUST
@page Defines a (optionally named) page formatting context. MUST MUST
@bottom-left-corner, @bottom-left,
@bottom-center, @bottom-right, @bottom-right-corner
Defines areas on the page within the running footer in the page’s bottom margin [CSS3PAGE] MUST MUST
@top-left-corner, @top-left,
@top-center,
@top-right,
@top-right-corner
Defines areas on the page within the running header in the page’s top margin [CSS3PAGE] MUST MUST

4. 4. Properties

As with selectors, the properties a printer MUST support are similar to those that a mobile device MUST support ([CSS-MOBILE], Properties) with the exception of those that don’t apply to the page or are specifically targeted at media other than the page.

In some cases the allowable values for a printer are a subset of the full range of values to match the reduced memory and performance capabilities of a low-cost printer.

The following table summarizes CSS Print Profile properties and property values. Refer to CSS Paged Media Level 3 [CSS3PAGE] for the definition of the size properties, CSS Image Values and Replaced Content Level 3 [CSS3-IMAGES] for the definition of the image-orientation, object-fit, and object-position properties, and CSS 2.1 [CSS21] for the definition of all other properties and values.

Name CSS Print CSS Print-Enhanced CSS Values Initial value
background background-color | inherit [background-color || background-image || background-repeat || background-position] | inherit [background-color || background-image || background-repeat || background-attachment || background-position] | inherit see individual properties
background-color MUST MUST <color> | transparent | inherit transparent
background-image MAY MUST <uri> | none | inherit none
background-position MAY MUST [ [ <percentage> | <length> ]{1,2} | [ [top | center | bottom] || [left | center | right] ] ] | inherit 0% 0%
background-repeat MAY MUST repeat | repeat-x | repeat-y | no-repeat | inherit repeat
border MAY MUST [ <border-width> || <border-style> || [<color> | transparent] ] | inherit see individual properties
border-collapse MAY MUST collapse | separate | inherit collapse
border-color MAY MUST [<color> | transparent]{1,4} | inherit see individual properties
border-spacing MAY MUST <length> <length>? | inherit 0
border-style MAY none, solid <border-style>{1,4} | inherit see individual properties
border-top border-right border-bottom border-left MAY MUST [ <border-width> || <border-style> || [<color> | transparent] ] | inherit see individual properties
border-top-color border-right-color border-bottom-color border-left-color MAY MUST <border-color> | transparent | inherit the value of the color property
border-top-style border-right-style border-bottom-style border-left-style MAY none, solid <border-style> | inherit none
border-top-width border-right-width border-bottom-width border-left-width MAY MUST <border-width> | inherit medium
border-width MAY MUST <border-width>{1,4} | inherit see individual properties
bottom MAY MUST <length> | <percentage> | auto | inherit auto
caption-side MAY MUST top | bottom | left | right | inherit top
clear MAY MUST none | left | right | both | inherit none
clip MAY MUST <shape> | auto | inherit auto
color MUST MUST <color> | inherit depends on user agent
content inherit | [<string> | counter(pages)]+ inherit | [<string> | counter(pages)]+ [ <string> | <uri> | <counter> | attr(X) | open-quote | close-quote | no-open-quote | no-close-quote ]+ | inherit empty string
counter-increment "pages" "pages" [ <identifier> <integer> ]+ | none | inherit none
counter-reset MUST MUST [ <identifier> <integer>? ]+ | none | inherit none
display MAY inline | block | list-item | none |inherit inline | block | list-item | run-in | compact | marker | table | inline-table | table-row-group | table-header-group | table-footer-group | table-row | table-column-group | table-column | table-cell | table-caption | none | inherit inline
object-fit MAY MUST fill | none | cover | contain fill
font [ [ font-style || font-weight ]? font-size [ / line-height ]? font-family ] | inherit [ [ font-style || font-variant || font-weight ]? font-size [ / line-height ]? font-family ] | inherit [ [ font-style || font-variant || font-weight ]? font-size [ / line-height ]? font-family ] | caption | icon | menu | message-box | small-caption | status-bar | inherit see individual properties
font-family MUST* MUST* [[ <family-name> | <generic-family> ],]* [ <family-name> | <generic-family> ] | inherit depends on user agent
font-size MUST ** MUST ** <absolute-size> | <relative-size> | <length> | <percentage> | inherit medium
font-style MUST** MUST ** normal | italic | oblique | inherit normal
font-variant MAY MUST normal | small-caps | inherit normal
font-weight MUST ** MUST ** normal | bold | bolder | lighter | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 | inherit normal
height MUST MUST <length> | <percentage> | auto | inherit auto
image-orientation MAY MUST <angle> | auto auto
left MAY MUST <length> | <percentage> | auto | inherit auto
letter-spacing MAY MUST normal | <length> | inherit normal
line-height MUST MUST normal | <number> | <length> | <percentage> | inherit normal
list-style MAY MUST [ list-style-type || list-style-position || list-style-image ] | inherit see individual properties
list-style-image MAY MUST <uri> | none | inherit none
list-style-position MUST MUST inside | outside | inherit outside
list-style-type disc, decimal, lower-alpha, upper-alpha, none and inherit disc, decimal, lower-alpha, upper-alpha, none and inherit disc | circle | square | decimal | decimal-leading-zero | lower-roman | upper-roman | lower-greek | lower-alpha | lower-latin | upper-alpha | upper-latin | hebrew | armenian | georgian | cjk-ideographic | hiragana | katakana | hiragana-iroha | katakana-iroha | none | inherit disc
margin MUST MUST <margin-width>{1,4} | inherit see individual properties
margin-top margin-right margin-bottom margin-left MUST MUST <margin-width> | inherit 0
object-position MAY MUST [ [<percentage> | <length> ]{1,2} | [ [top | center | bottom] || [left | center | right] ] ] 50% 50%
float MAY MUST left | right | none | inherit none
orphans MAY MUST <integer> | inherit 2
overflow MAY MUST visible | hidden | scroll | auto | inherit visible
padding MAY MUST <padding-width>{1,4} | inherit see individual properties
padding-top padding-right padding-bottom padding-left MAY MUST <padding-width> | inherit 0
page MUST MUST <identifier> | auto auto
page-break-after auto | always | inherit auto | always | inherit auto | always | avoid | left | right | inherit auto
page-break-before auto | always | inherit auto | always | inherit auto | always | avoid | left | right | inherit auto
page-break-inside MUST MUST avoid | auto | inherit auto
position MAY MUST static | relative | absolute | fixed | inherit static
right MAY MUST <length> | <percentage> | auto | inherit auto
size [<length>{1,2}| letter | legal | ledger | A4 | A5 | A3 | B4 | B5 ] | auto | portrait | inherit [<length>{1,2} | letter | legal | ledger | A4 | A5 | A3 | B4 | B5 ] | auto | portrait | landscape | inherit [<length>{1,2} | letter | legal | ledger | A4 | A5 | A3 | B4 | B5 ] | auto | portrait | landscape | inherit auto
table-layout MAY MUST auto | fixed | inherit auto
text-align left | center | inherit left | right | center | inherit left | right | center | justify | <string> | inherit depends on user agent and writing direction
text-decoration none, underline, and inherit none, underline, and inherit none | [ underline || overline || line-through || blink ] | inherit none
text-indent MUST MUST <length> | <percentage> | inherit 0
text-transform MAY MUST capitalize | uppercase | lowercase | none | inherit none
top MAY MUST <length> | <percentage> | auto | inherit auto
vertical-align MAY MUST1 baseline | sub | super | top | text-top | middle | bottom | text-bottom | <percentage> | <length> | inherit baseline
visibility MAY MUST visible | hidden | collapse | inherit inherit
white-space MUST MUST normal | pre | nowrap | inherit normal
widows MAY MUST <integer> | inherit 2
width MUST MUST <length> | <percentage> | auto | inherit auto

Table Note:

† Only the single identifier "pages" that represents the current page number is REQUIRED.

* It is RECOMMENDED that a printer minimally support "serif," "sans-serif," and "monospace" font families.

** The supported values SHOULD be appropriate to the fonts available to the printer.

‡ The printer MAY ignore positioned elements that are placed on the page before the position of the current element in the normal flow.

1 Vertical alignment is undefined across page boundaries.

4.1. Image Rendering Properties

A previous Working Draft of this document defined fit and fit-position properties.

To support legacy content using these properties, implementations of the CSS Print Profile MAY alias the object-fit and object-position properties as defined below:

Property/Value Alias
object-fit fit
none hidden
cover slice
contain meet
object-position fit-position

Additionally, implementations MAY override initial value of object-position (which is '50% 50%') to be '0% 0%' by adding an appropriate rule to the UA style sheet, if that is required for compatibility with existing content. Similarly, if inheritance is required, then that may also be indicated by UA style sheet rule.

The following rule positions all images with object-fit values other than fill to be top-left aligned:

* { object-position: top left; }

The following rules also cause object-position to inherit.

* { object-position: inherit; }:root { object-position: top left; }

5. 5. CSS Syntax

The CSS Print Profile uses the same syntax as specified in Cascading Style Sheets, Level 2, revision 1 (CSS 2.1) [CSS21]. The CSS Print Profile uses a subset of the values used in CSS 2.1. Specifically:

  1. The printer SHALL support integer and real numbers ([CSS21], Section 4.3.1).
  2. The printer SHALL support the following lengths ([CSS21], Section 4.3.2):
    • px
    • em
    • ex
    • in
    • cm
    • mm
    • pt
    • pc
    The printer MAY support other lengths.
  3. The printer SHALL support percentage values ([CSS21], Section 4.3.3).
  4. The printer SHALL support URI values ([CSS21], Section 4.3.4).
  5. The printer SHALL support a "pages" counter value that tracks page numbers ([CSS21], Section 4.3.5).
  6. The printer SHALL support the following color values: The printer MAY support other color values. The printer MAY support user preferences for colors ([CSS21], Section 18.2).
  7. The printer MAY support user preferences for fonts ([CSS21], Section 18.3).

Similarly, the CSS Print Profile requires that conforming user agents support the character encoding mechanisms specified in CSS 2.1 [CSS21]. Specifically:

  1. The printer SHALL support priorities specified in CSS 2.1 [CSS21] to determine a document’s character encoding.
  2. The printer SHALL support the CSS 2.1 @charset rules. However, if the character set specified by the @charset rule of a external style sheet is not supported by the printer, the style sheet will be ignored.

6. 6. Assigning Property Values, Cascading, and Inheritance

In general, the CSS Print Profile uses the same cascading rules as in CSS 2.1. Specifically:

  1. The printer SHALL assign values as described in CSS 2.1 ([CSS21], Section 6.1).
  2. The printer SHALL support inheritance as described in CSS 2.1 ([CSS21], Section 6.2).
  3. A printer supporting Enhanced Layout Extension conformance SHALL support the CSS 2.1 @import rules as specified in CSS 2.1 ([CSS21], Section 6.3).
  4. The printer SHALL support author style sheets. The printer MAY support user or user-agent style sheets ([CSS21], Section 6.4).
  5. The printer SHALL support all CSS 2.1 cascading mechanisms ([CSS21] Sections 6.4.1-6.4.4).

7. 7. Media Types

A CSS Print Profile conforming user agent SHALL be able to process media-dependent style sheets as specified in CSS 2.1 ([CSS21], Section 7). Specifically:

  1. The printer SHALL support the CSS 2.1 @media rules as specified in CSS 2.1 ([CSS21], Section 7).
  2. The printer SHALL accept and process style sheets that target the print media type.
  3. The printer SHALL accept and process style sheets that target the all media type.
  4. The printer SHALL accept style sheets that contain other (non-print) media-dependent style sheets.
  5. The printer MAY process other media types (such as projection or handheld).

8. 8. CSS Print Profile Properties and User Agent interactions

The following sections relax or otherwise modify the conformance requirements.

8.1. 8.1 Nested Floats, Divs, and Absolutely Positioned Boxes

Authors are cautioned that the nesting of floats, divs, and absolutely positioned boxes within themselves, each other, and table cells should be used carefully, since the nesting depth of these constructs is printer and implementation dependent.

8.2. 8.2 Page Breaks

If page-break-inside: avoid is specified for a long element and the printer is unable to buffer the entire element before committing it to paper, it SHOULD force a page break to occur before the long element and begin the element starting at the top of the next page. If the long element starts at the top of a page and exceeds the page length, the printer SHALL print as much as possible on the first page and then resume that element on the next and subsequent pages as REQUIRED to preserve the content. A printer MAY perform scaling to fit the long element on a single page; but this is not recommended unless the scaling required is minimal.

8.3. 8.3 Page Size

Due to a printer’s mechanical limitations, the actual printable area of the page is often less than the page size.  However, a printer SHOULD be guided by the page size value supplied by the CSS size property when choosing the media to print on.

See http://www.w3.org/TR/css3-page/#renderingpages in CSS3 Paged Media [CSS3PAGE] for a discussion of fitting contents to media sheets.

8.4. 8.4 Default Style Sheets

This entire section is informative.

Appendix D of Cascading Style Sheets, Level 2, revision 1 ([CSS21], Appendix D) provides a sample style sheet. This sheet uses several properties that are not required of a conforming printer, even ones supporting the enhanced layout extensions (section 2.1).

8.4.1. 8.5.1 Default Style Sheet Guidelines for printers

Developers of printers that do not implement the enhanced layout facilities are encouraged but not required to adhere to the following implementation guidelines that address unsupported properties. These guidelines are presented to promote consistency between printer implementations.

The guidelines below are annotated to show derivation of the guideline from the Cascading Style Sheets, Level 2, revision 1 [CSS21] style sheet.

  1. The address, blockquote, body, dd, div, dl, dt, h1, h2, h3, h4, h5, h6, hr, object, ol, p, pre, and ul elements should be treated as if their display property were set to block.
  2. The li element should be treated as if its display property were set to list-items.
  3. The table elements, table, tr, td, th, and caption, should have their standard meaning and display treatments: table, table-row, table-cell, and table-caption.
  4. The elements base, br, html, head, link, meta, param, style and title should be treated as if their display property were set to none.
  5. The remaining elements, a, abbr, acronym, b, big, cite, code, dfn, em, form, i, img, input, kbd, option, samp, small, select, strong, sub, sup, textarea, tt, and var, should be treated as if their display property were set to inline. A display property of inline for the elements img, input, select, and textarea allows document authors a flexibility not available if their display property were block.
    The above guidelines come from the following portion of the CSS 2.1 default style sheet:
    ADDRESS, BLOCKQUOTE, BODY, DD, DIV, DL, DT, FIELDSET, FORM, 
    FRAME, FRAMESET, H1, H2, H3, H4, H5, H6, IFRAME, NOFRAMES, 
    OBJECT, OL, P, UL, APPLET, CENTER, DIR, HR, MENU, 
                  { display: block }
    LI            { display: list-item }
    HEAD          { display: none }
    TABLE         { display: table }
    TR            { display: table-row }
    THEAD         { display: table-header-group }
    TBODY         { display: table-row-group }
    TFOOT         { display: table-footer-group }
    COL           { display: table-column }
    COLGROUP      { display: table-column-group }
    TD, TH        { display: table-cell }
    CAPTION       { display: table-caption } 
    
  6. The edges of the content of body element should have 0.1 inch wide inset from the left, top, right, and bottom of the printable area of the page. Margin calculations will start from these offsets.
    The .1 inch figure comes from the calculation that 8 px divided by 75px/inch ( a normal display resolution) is about .1 inches.
    BODY          { padding: 8px; 
                    line-height: 1.33 } 
    
  7. The content of the sub element should be treated as if its vertical-align property were set to sub. Similarly, the content of the sup element should be treated as if its vertical-align property were set to sup.
    SUB             { vertical-align: sub }
    SUP             { vertical-align: super } 
    
  8. The hr element should be treated as if its area, as defined by its height and width, were outlined by a one pixel thick, solid line. The default line should be one pixel high and the width of the containing box.
    HR              { border: 1px inset } 
    
  9. The lower case letters of the content of the abbr and acronym elements should be rendered as scaled capital letters, at approximately 75% of their size at the current font size. Upper case letters will be unchanged. Printers may also choose to simply render lower case letters as upper case letters without scaling.
    The 75% figure above is only one way to approximate small-caps. The printer is free to use its own rendering of small-caps.
    ABBR, ACRONYM   { font-variant: small-caps; 
                      letter-spacing: 0.1em } 
    
  10. Page break avoidance both inside and after is removed for the elements h1, h2, h3, h4, h5, and h6. Therefore, the printer is not required to move the content of these elements from the bottom of one page to the top of the next.
    H1, H2, H3,
    H4, H5, H6    { page-break-after: avoid; 
                    page-break-inside: avoid }
    
  11. The printer need not avoid page breaks before the ul, ol, and dl elements.
    UL, OL, DL    { page-break-before: avoid } 
    
  12. The printer may choose its own, fixed value for the padding properties of elements where the Cascading Style Sheets, Level 2, revision 1 box model ([CSS21], Section 8) applies.
  13. The content of all elements, except hr, should be treated as if the element’s border-style property were set to none.
  14. The content of all elements may be treated as if the element’s overflow property were set to visible and the clip property set to auto.
    This guideline suggests consistent behavior among implementations.
  15. The content of all elements may be treated as if the element’s positioning property were set to static.
    Elements should be treated as if they are in the normal flow.
  16. Tables should be treated as if the table-layout property were set to fixed.
    This guideline promotes consistency since
    • the table-layout property is not mandated
    • There isn’t a CSS default style sheet rule for this property

The following style sheet is a modification of the sample sheet in Appendix D of Cascading Style Sheets, Level 2, revision 1 ([CSS21], Appendix D) and depends on the above guidelines.

th              { font-weight: bolder; text-align: center }caption         { text-align: center }
body            { line-height: 1.33 }
h1              { font-size: 2em; margin: .67em 0 }
h2              { font-size: 1.5em; margin: .83em 0 }
h3              { font-size: 1.17em; margin: 1em 0 }
h4, p,
blockquote, ul,
form,
ol, dl          { margin: 1.33em 0 }
h5              { font-size: .83em; line-height: 1.17em; margin: 1.67em 0 }
h6              { font-size: .67em; margin: 2.33em 0 }
h1, h2, h3, h4,
h5, h6, b,
strong          { font-weight: bolder }
blockquote      { margin-left: 40px; margin-right: 40px }
i, cite, em,
var, address    { font-style: italic }
pre, tt, code,
kbd, samp       { font-family: monospace }
pre             { white-space: pre }
big             { font-size: 1.17em }
small, sub, sup { font-size: .83em }
ol, ul, dd      { margin-left: 40px }
ol              { list-style-type: decimal }
ol ul, ul ol,
ul ul, ol ol    { margin-top: 0; margin-bottom: 0 }
br       { content: "\A" }

@media print {
  @page         { margin: 10% }
  blockquote, 
  pre           { page-break-inside: avoid }
}

8.4.2. 8.5.2 Default Style Sheet Guidelines for Enhanced Layout printers

Developers of printers conforming to the enhanced layout extensions (section 2.1) MUST implement more of Cascading Style Sheets, Level 2, revision 1 [CSS21] than conforming printers, although the set of properties and their values is still less than complete.

Developers of printers are encouraged but not required to adhere to the following implementation guidelines that address unsupported properties.

  1. The table elements, table, tr, td, th, and caption, should have their standard meaning and display treatments: table, table-row, table-cell, and table-caption.
  2. The rendering of the hr element is implementation dependent since support of the inset value of the border-style property is not required.
  3. Page break avoidance both inside and after is removed for the elements h1, h2, h3, h4, h5, and h6. Therefore, the printer need not be concerned with moving the content of these elements from the bottom of one page to the top of the next.
  4. The printer need not avoid page breaks before the ul, ol, and dl elements.

The following style sheet is a modification of the sample sheet in Appendix D of [CSS21] and depends on the above guidelines.

address,blockquote, 
body, dd, div, 
dl, dt, 
form,
h1, h2, h3, h4, 
h5, h6, 
object, ol, p, 
ul,
hr, pr e        { display: block }
li              { display: list-item }
head            { display: none }
th              { font-weight: bolder; text-align: center }
caption         { text-align: center }
body            { padding: 8px; line-height: 1.33 }
h1              { font-size: 2em; margin: .67em 0 }
h2              { font-size: 1.5em; margin: .83em 0 }
h3              { font-size: 1.17em; margin: 1em 0 }
h4, p,
blockquote, ul,
form,
ol, dl,         { margin: 1.33em 0 }
h5              { font-size: .83em; line-height: 1.17em; margin: 1.67em 0 }
h6              { font-size: .67em; margin: 2.33em 0 }
h1, h2, h3, h4,
h5, h6, b,
strong          { font-weight: bolder }
blockquote      { margin-left: 40px; margin-right: 40px }
i, cite, em,
var, address    { font-style: italic }
pre, tt, code,
kbd, samp       { font-family: monospace }
pre             { white-space: pre }
big             { font-size: 1.17em }
small, sub, sup { font-size: .83em }
hr              { border: 1px  }
ol, ul, dd      { margin-left: 40px }
ol              { list-style-type: decimal }
ol ul, ul ol,
ul ul, ol ol    { margin-top: 0; margin-bottom: 0 }
br       { content: "\A" }

@media print {
  @page         { margin: 10% }
  blockquote, 
  pre           { page-break-inside: avoid }
}

9. 9. Acknowledgements

This section is informative.

This specification was prepared by the W3C CSS Working Group.

This specification is based on the specification of the same name, CSS Print Profile [CSSPP] from the Printer Working Group, a program of and through the IEEE Industry Standards and Technology Organization, Inc. The editor wishes to express her gratitude to all those who contributed to it.

Conformance

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.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
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.

Requirements for Responsible Implementation of CSS

The following sections define several conformance requirements for implementing CSS responsibly, in a way that promotes interoperability in the present and future.

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 property 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.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Implementations of CR-level Features

Once a specification reaches the Candidate Recommendation stage, implementers should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec, and should avoid exposing a prefixed variant of that feature.

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.

Index

Terms defined by reference

References

Normative References

[CSS-BACKGROUNDS-3]
CSS Backgrounds and Borders Module Level 3 URL: https://drafts.csswg.org/css-backgrounds-3/
[CSS-BREAK-3]
Rossen Atanassov; Elika Etemad. CSS Fragmentation Module Level 3. URL: http://dev.w3.org/csswg/css-break/
[CSS-CONTENT-3]
Elika Etemad; Dave Cramer. CSS Generated Content Module Level 3. URL: https://drafts.csswg.org/css-content/
[CSS-FONTS-3]
John Daggett. CSS Fonts Module Level 3. URL: http://dev.w3.org/csswg/css-fonts/
[CSS-IMAGES-3]
CSS Image Values and Replaced Content Module Level 3 URL: https://drafts.csswg.org/css-images-3/
[CSS-LISTS-3]
Tab Atkins Jr.. CSS Lists and Counters Module Level 3. URL: http://dev.w3.org/csswg/css3-lists/
[CSS-MASKING-1]
Dirk Schulze; Brian Birtles; Tab Atkins Jr.. CSS Masking Module Level 1. URL: http://dev.w3.org/fxtf/css-masking-1/
[CSS-OVERFLOW-4]
CSS Overflow Module Level 4 URL: https://drafts.csswg.org/css-overflow-4/
[CSS-PAGE-3]
CSS Paged Media Module Level 3 URL: https://drafts.csswg.org/css-page-3/
[CSS-POSITION-3]
Rossen Atanassov; Arron Eicholz. CSS Positioned Layout Module Level 3. URL: https://drafts.csswg.org/css-position/
[CSS-TEXT-3]
Elika Etemad; Koji Ishii. CSS Text Module Level 3. URL: http://dev.w3.org/csswg/css-text-3/
[CSS-TEXT-DECOR-3]
Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 3. URL: http://dev.w3.org/csswg/css-text-decor-3/
[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: https://www.w3.org/TR/CSS2
[CSS22]
Bert Bos. Cascading Style Sheets Level 2 Revision 2 (CSS 2.2) Specification. URL: http://dev.w3.org/csswg/css2/
[CSS3-IMAGES]
Elika Etemad; Tab Atkins Jr.. CSS Image Values and Replaced Content Module Level 3. 17 April 2012. CR. URL: https://www.w3.org/TR/css3-images/
[CSS3PAGE]
Melinda Grant; et al. CSS Paged Media Module Level 3. 14 March 2013. WD. URL: https://www.w3.org/TR/css3-page/
[HTML401]
Dave Raggett; Arnaud Le Hors; Ian Jacobs. HTML 4.01 Specification. 24 December 1999. REC. URL: https://www.w3.org/TR/html401
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119

Informative References

[CSS-MOBILE]
Bert Bos. CSS Mobile Profile 2.0. 14 October 2014. NOTE. URL: https://www.w3.org/TR/css-mobile
[CSSPP]
D. Wright; J. Bigelow, eds.. CSS Print Profile. 28 March 2003. Proposed Standard 5102.2. URL: http://www.pwg.org/xhtml-print/HTML-Version/CSS-Print.html
[XHTML-PRINT]
Shane McCarron. XHTML-Print - Second Edition. 23 November 2010. REC. URL: https://www.w3.org/TR/xhtml-print