ITU-T H 763 1-2010 Cascading style sheets for IPTV services (Study Group 16)《IPTV服务的级联样式表(研究组16)》.pdf

1、 International Telecommunication Union ITU-T H.763.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/2010) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSIPTV multimedia services and applications for IPTV IPTV multimedia application frameworks Cascading style sheets for IPTV services Recommendation

2、ITU-T H.763.1 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects H.230H.239 Communication procedure

3、s H.240H.259 Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for audiovisual and multimedia servi

4、ces H.360H.369 Supplementary services for multimedia H.450H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile multimedia collaboration applications

5、 and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559 Mobile multimedia collaboration inter-working procedures H.560H.569 BROADBAND, TRIPLE-

6、PLAY AND ADVANCED MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 Advanced multimedia services and applications H.620H.629 IPTV MULTIMEDIA SERVICES AND APPLICATIONS FOR IPTV General aspects H.700H.719 IPTV terminal devices H.720H.729 IPTV middleware H.730H.739 IPTV application

7、 event handling H.740H.749 IPTV metadata H.750H.759 IPTV multimedia application frameworks H.760H.769IPTV service discovery up to consumption H.770H.779 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.763.1 (09/2010) i Recommendation ITU-T H.763.1 Cascading style

8、 sheets for IPTV services Summary Recommendation ITU-T H.763.1 describes cascading style sheets (CSS) for IPTV. The CSS profile presented in this Recommendation provides the means for describing the presentation style of documents relative to IPTV terminal devices. This profile is based on CSS 1, a

9、part of CSS 2 and a number of extended properties required for IPTV services. CSS is human readable and writable, and expresses style in common desktop publishing terminology. History Edition Recommendation Approval Study Group 1.0 ITU-T H.763.1 2010-09-13 16 ii Rec. ITU-T H.763.1 (09/2010) FOREWORD

10、 The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying tec

11、hnical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which

12、, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and I

13、EC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to e

14、nsure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words d

15、oes not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concern

16、ing the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by pate

17、nts, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2011 All rights reserved. No part of this publi

18、cation may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T H.763.1 (09/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 1 4 Abbreviations and acronyms 1 5 Introdu

19、ction 2 6 Syntax and basic data types 2 7 Selectors 2 7.1 Universal selector . 2 7.2 Type selectors . 2 7.3 Class selectors 3 7.4 ID selectors . 3 7.5 The dynamic pseudo-classes: :active and :focus . 3 8 Properties 3 8.1 Assigning property values, cascading, and inheritance 3 8.2 Box model 4 8.3 Vis

20、ual formatting model . 7 8.4 Visual formatting model details . 9 8.5 Visual effects 10 8.6 Colours and backgrounds . 11 8.7 Fonts . 14 8.8 Text . 16 8.9 Extended properties for IPTV 17 Annex A Colour index for common colours . 21 Annex B Default style sheet . 25 Rec. ITU-T H.763.1 (09/2010) 1 Recomm

21、endation ITU-T H.763.1 Cascading style sheets for IPTV services 1 Scope This Recommendation describes cascading style sheets to provide interoperability and harmonization among IPTV multimedia application frameworks. To provide global standard IPTV services, it is foreseeable that a combination of d

22、ifferent standard multimedia application frameworks will be used. Therefore, this Recommendation describes cascading style sheets, as one of those standard multimedia application frameworks, to provide interoperable use of IPTV services. 2 References The following ITU-T Recommendations and other ref

23、erences contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to in

24、vestigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the

25、status of a Recommendation. ITU-T H.762 Recommendation ITU-T H.762 (2009), Lightweight interactive multimedia environment (LIME) for IPTV services. CSS1 World Wide Web Consortium (W3C) (1996), Cascading Style Sheets, level 1. CSS2 World Wide Web Consortium (W3C) (1998), Cascading Style Sheets, level

26、 2 CSS2 Specification. 3 Definitions 3.1 Terms defined elsewhere None. 3.2 Terms defined in this Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: BML Broadcasting Markup Language CLUT Colour Look-Up Table CSS Cascading Style Sheets

27、HTML HyperText Markup Language N/A Not Applicable SVG Scalable Vector Graph UA User Agent URI Universal Resource Identifier 2 Rec. ITU-T H.763.1 (09/2010) W3C World Wide Web Consortium XML Extensible Markup Language 5 Introduction CSS is a style sheet language specified by W3C that is used to descri

28、be the presentation (e.g., fonts, colours and spacing) of a document written in a markup language. CSS is human readable and writable, and expresses style in common desktop publishing terminology. CSS has been in use since October 1995 using the media type text/css without registration. A CSS can be

29、 either linked to a document through a URI or included in the document. CSS does not constitute by itself a multimedia framework, but is used with some markup languages such as the one defined in ITU-T H.762. This Recommendation gives the core functionalities of CSS for IPTV services. 6 Syntax and b

30、asic data types The syntax for cascading style sheets is described in Appendix B of CSS1. The default style sheet describing the features of the profile specified in this Recommendation is given in Annex B herein. 7 Selectors In CSS, selectors are patterns used in pattern matching rules that determi

31、ne which style rules apply to elements in the document tree. Selectors may range from simple element names to rich contextual patterns. If all conditions in the pattern are true for a certain element, the selector matches the element. Table 7-1 summarizes the selector syntax of this Recommendation:

32、Table 7-1 The syntax of selectors Pattern Meaning Described in clause * Matches any element. Universal selector E Matches any E element (i.e., an element of type E). Type selectors E:active E:focus Matches E during certain user actions. Dynamic pseudo-classes DIV.warning Language specific (in HTML,

33、the same as DIVclass=“warning“) Class selectors E#myid Matches any E element with ID equal to “myid“. ID selectors 7.1 Universal selector The universal selector, written “*“, matches the name of any element type. It matches any single element in the document tree. If the universal selector is not th

34、e only component of a simple selector, the “*“ may be omitted. 7.2 Type selectors A type selector matches the name of a document language element type. A type selector matches every instance of the element type in the document tree. Rec. ITU-T H.763.1 (09/2010) 3 7.3 Class selectors The period (.) n

35、otation may be used for HTML as an alternative to the = notation when representing the class attribute. Thus, for HTML, div.value and divclass=value have the same meaning. The attribute value must immediately follow the “period“ (.). UAs may apply selectors using the period (.) notation in XML docum

36、ents if the UA has namespace specific knowledge that allows it to determine which attribute is the “class“ attribute for the respective namespace. 7.4 ID selectors An ID attribute can be used to uniquely identify its element, regardless of the document language, e.g., HTML or XML. In HTML all ID att

37、ributes are named “id“; XML applications may name ID attributes differently. In any document language, no two attributes of type ID can have the same value. The ID attribute of a document language allows authors to assign an identifier to one element instance in the document tree. CSS ID selectors m

38、atch an element instance based on its identifier. A CSS ID selector contains a “#“ immediately followed by the ID value, which must be an identifier. 7.5 The dynamic pseudo-classes: :active and :focus Interactive user agents sometimes change the rendering in response to user actions. CSS provides tw

39、o pseudo-classes for common cases: The :active pseudo-class applies while an element is being activated by the user. For example, between the times the user presses the mouse button and releases it. The :focus pseudo-class applies while an element has the focus (accepts keyboard events or other form

40、s of text input). 8 Properties The following is the list of properties defined in this Recommendation. media left* background-image margin top* background-repeat padding-top width* font-family padding-right height* font-size padding-bottom z-index font-weight padding-left line-height text-align bord

41、er-width display letter-spacing border-style visibility white-space position overflow NOTE For property values with “*“, the elements , , , and must have these property values. The elements , , must not have these property values. 8.1 Assigning property values, cascading, and inheritance 8.1.1 Media

42、 types One of the most important features of style sheets is that they specify how a document is to be presented on different media: on the screen, on paper, with a speech synthesizer, with a Braille device, etc. Certain CSS properties are only designed for certain media (e.g., the page-break-before

43、 property only applies to paged media). On occasion, however, style sheets for different media types may 4 Rec. ITU-T H.763.1 (09/2010) share a property, but require different values for that property. For example, the font-size property is useful both for screen and print media. The two media types

44、 are different enough to require different values for the common property; a document will typically need a larger font on a computer screen than on paper. Therefore, it is necessary to express that a style sheet, or a section of a style sheet, applies to certain media types. 8.1.1.1 The media rule

45、An media rule specifies the target media types (separated by commas) of a set of rules (delimited by curly braces). The media construct allows style sheet rules for various media in the same style sheet: media print body font-size: 10pt media screen body font-size: 13px media screen, print body line

46、-height: 1.2 8.2 Box model The CSS box model describes the rectangular boxes that are generated for elements in the document tree and laid out according to the visual formatting model. 8.2.1 Margin properties: margin Margin properties specify the width of the margin area of a box. The margin shortha

47、nd property sets the margin for all four sides while the other margin properties only set their respective side. These properties apply to all elements, but vertical margins will not have any effect on non-replaced inline elements. Table 8-1 The margin property Value: 0 Initial: See individual prope

48、rties Applies to: All elements except elements with table display types other than table-caption, table and inline-table Inherited: No Percentages: Refer to width of containing block Media: Visual Computed value: See individual properties The margin property is a shorthand property for setting margi

49、n-top, margin-right, margin-bottom, and margin-left at the same place in the style sheet. If there is only one value, it applies to all sides. If there are two values, the top and bottom margins are set to the first value and the right and left margins are set to the second. If there are three values, the top is set to the first value, the left and right are set to the second, and the bottom is set to the third. If there are four values, they apply to the to