W3C CSS2 Cascading Style Sheets, level 2 - instructional media + ...

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15.4 Font Characteristics 15.4.1 Introducing Font Characteristics In this section are listed the font characteristics that have been found useful for client-side font matching, synthesis, and download for heterogeneous platforms accessing the Web. The data may be useful for any medium that needs to use fonts on the Web by some other means than physical embedding of the font data inside the medium. These characteristics are used to characterize fonts. They are not specific to CSS, or to style sheets. In CSS, each characteristic is described by a font descriptor. These characteristics could also be mapped onto VRML nodes, or CGM Application Structures, or a Java API, or alternative style sheet languages. Fonts retrieved by one medium and stored in a proxy cache could be re-used by another medium, saving download time and network bandwidth, if a common system of font characteristics are used throughout. A non-exhaustive list of examples of such <strong>media</strong> includes: 2-D vector formats Computer Graphics Metafile Simple Vector Format 3-D graphics formats VRML 3DMF Object embedding technologies Java Active-X Obliq 15.4.2 Full font name This is the full name of a particular face of a font family. It typically includes a variety of non-standardized textual qualifiers or adornments appended to the font family name. It may also include a foundry name or abbreviation, often prepended to the font family name. It is only used to refer to locally installed fonts, because the format of the adorned name can vary from platform to platform. It must be quoted. For example, the font family name of the TrueType font and the PostScript name may differ in the use of space characters, punctuation, and in the abbreviation of some words (e.g., to meet various system or printer interpreter constraints on length of names). For example, spaces are not allow in a PostScript name, but are common in full font names. The TrueType name table can also contain the PostScript name, which has no spaces. The name of the font definition is important because it is the link to any locally installed fonts. It is important that the name be robust, both with respect to platform and application independence. For this reason, the name should be one that is not application- or language-specific. 226
The ideal solution would be to have a name that uniquely identifies each collection of font data. This name does not exist in current practice for font data. Fonts with the same face name can vary over a number of descriptors. Some of these descriptors, such as different complements of glyphs in the font, may be insignificant if the needed glyphs are in the font. Other descriptors, such as different width metrics, make fonts with the same name incompatible. It does not seem possible to define a rule that will always identify incompatibilities, but will not prevent the use of a perfectly suitable local copy of the font data with a given name. Therefore, only the range of ISO 10646 characters will be used to qualify matches for the font face name. Since a prime goal of the font face name in the font definition is to allow a user agent to determine when there is a local copy of the specified font data, the font face name must be a name that will be in all legitimate copies of the font data. Otherwise, unnecessary Web traffic may be generated due to missed matches for the local copy. 15.4.3 Coordinate units on the em square Certain values, such as width metrics, are expressed in units that are relative to an abstract square whose height is the intended distance between lines of type in the same type size. This square is called the em square and it is the design grid on which the glyph outlines are defined. The value of this descriptor specifies how many units the EM square is divided into. Common values are for example 250 (Intellifont), 1000 (Type 1) and 2048 (TrueType, TrueType GX and Open- Type). If this value is not specified, it becomes impossible to know what any font metrics mean. For example, one font has lowercase glyphs of height 450; another has smaller ones of height 890! The numbers are actually fractions; the first font has 450/1000 and the second has 890/2048 which is indeed smaller. 15.4.4 Central Baseline This gives the position in the em square [p. 227] of the central baseline. The central baseline is used by ideographic scripts for alignment, just as the bottom baseline is used for Latin, Greek, and Cyrillic scripts. 15.4.5 Font Encoding Either explicitly or implicitly, each font has a table associated with it, the font encoding table, that tells what character each glyph represents. This table is also referred to as an encoding vector. In fact, many fonts contain several glyphs for the same character. Which of those glyphs should be used depends either on the rules of the language, or on the preference of the designer. In Arabic, for example, all letters have four (or two) different shapes, depending on whether the letter is used at the start of a word, in the middle, at the end, or in isolation. It is the same character in all cases, and thus there is only one character in the source document, but when printed, it looks different each time. 227
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REC-CSS2-19980512 Cascading Style S
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Quick Table of Contents 1 About the
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4.3.4 URL + URN = URI . . . . . . .
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9.7 Relationships between ’displa
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cursive . . . . . . . . . . . . . 2
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B.1 New functionality . . . . . . .
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Section 2: An introduction to CSS2
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Initial This part specifies the pro
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The section on Paged Media was in l
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Contents 2 Introduction to CSS2 2.1
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CSS2 has more than 100 different pr
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Adding more rules to the style shee
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Simplicity. CSS2 is more complex th
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Document language The encoding lang
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3.2 Conformance This section define
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Contents 4 CSS2 syntax and basic da
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Macro Definition ident name nmstart
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In fact, these two methods may be c
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P[example="public class foo\ {\ pri
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A user agent conforming to a future
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0.28 mm 1.4 mm viewer 28 inch 71 cm
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Example(s): An example without quot
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Values outside the device gamut sho
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When a style sheet resides in a sep
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Contents 5 Selectors 5.1 Pattern ma
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5.2 Selector syntax A simple select
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5.6 Child selectors A child selecto
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Example(s): The following rule hide
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H1#chapter1 { text-align: center }
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Example(s): The following rule sets
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5.11.4 The language pseudo-class: :
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The following CSS2 will make a drop
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6 Assigning property values, Cascad
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BODY { font-size: 10pt } H1 { font-
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6.4.1 Cascading order To find the v
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author style sheet and may be overr
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Link to a target medium The bo
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Relationship between media groups a
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Top TM TB TP Margin (Transparent) B
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First element of list Second elemen
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Value: {1,4} | inherit Initial: not
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values, they apply to the top, righ
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’border-color’ Value: {1,4} | t
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Since the initial value of the bord
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Contents 9 Visual formatting model
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9.2 Controlling box generation The
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The P generates a block box, with s
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The properties of the run-in elemen
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Value: static | relative | absolute
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The offset is a fixed distance from
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or like this: Several emphasized wo
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IMG { float: left } BODY, P, IMG {
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image margin paragraph border parag
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Values have the following meanings
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position: fixed; width: 100%; heigh
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Document Window (0,0) (0, 400) 1 Be
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Document Window (0,0) (0, 400) 24 p
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Document Window I used two red hyph
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This text will be beneath everythi
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(U+202C) at the end of the element.
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Contents 10 Visual formatting model
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#div1 { position: absolute; left: 5
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(If the border style is ’none’,
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’max-width’ Value: Initial: App
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10.6.1 Inline, non-replaced element
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Value: Initial: Applies to: | | n
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. We recommend a computed value for
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Contents 11 Visual effects 11.1 Ove
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DIV I didn’t like the play, but t
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(0, 0) (50, 0) clip region (0, 55)
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onclick=’show("container2");hid
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12 Generated content, automatic num
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the pseudo-element will behave as i
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’block’: the pseudo-element is
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Approximate rendering ISO 10646 cod
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Value: [ ? ]+ | none | inherit Ini
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Example(s): The following style she
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first or last line box exists in a
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This is a very short document. This
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decimal Decimal numbers, beginning
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inside The marker box is the first
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OL.alpha { list-style: lower-alpha
Page 175 and 176: Contents 13 Paged media 13.1 Introd
Page 177 and 178: Sheet Page box A D Page content B C
Page 179 and 180: 13.2.3 Crop marks: the ’marks’
Page 181 and 182: 13.3.1 Break before/after elements:
Page 183 and 184: Value: | inherit Initial: 2 Applie
Page 185 and 186: 13.4 Cascading in the page context
Page 187 and 188: Contents 14 Colors and Backgrounds
Page 189 and 190: This property sets the background i
Page 191 and 192: User agents may treat ’fixed’ a
Page 193 and 194: 14.3 Gamma correction For informati
Page 195 and 196: Contents 15 Fonts 15.1 Introduction
Page 197 and 198: In the CSS2 font model, as in CSS1,
Page 199 and 200: 15.2.2 Font family: the ’font-fam
Page 201 and 202: normal font. italic Specifies a fon
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Page 205 and 206: Specifies the aspect value. The num
Page 207 and 208: 15.2.5 Shorthand font property: the
Page 209 and 210: menu The font used in menus (e.g.,
Page 211 and 212: Latin fonts Greek fonts Cyrillic fo
Page 213 and 214: page can be displayed. Progressive
Page 215 and 216: 15.3.2 Descriptors for Selecting a
Page 217 and 218: 15.3.3 Descriptors for Font Data Qu
Page 219 and 220: Value: [ [format( [, ]*)] | ] [,
Page 221 and 222: ’stemv’ (Descriptor) Value: In
Page 223 and 224: the extras are ignored. [p. 42] Exa
Page 225: Swiss 721 light Swiss 721 Swiss 721
Page 229 and 230: 15.4.11 Lower Baseline This gives t
Page 231 and 232: 15.4.19 Vertical stem width This is
Page 233 and 234: The per-descriptor matching rules f
Page 235 and 236: The next example defines a family o
Page 237 and 238: Contents 16 Text 16.1 Indentation:
Page 239 and 240: 16.3.1 Underlining, overlining, str
Page 241 and 242: Example(s): Consider this example:
Page 243 and 244: This property controls capitalizati
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Page 249 and 250: ’table-footer-group’) element T
Page 251 and 252: caption’s margin caption caption
Page 253 and 254: current margins text text text prev
Page 255 and 256: cells rows row groups columns colum
Page 257 and 258: The two algorithms are described be
Page 259 and 260: percentage values of ’height’ r
Page 262 and 263: The lengths specify the distance th
Page 264 and 265: order−width padding padding borde
Page 266 and 267: An example of a table with collapse
Page 268 and 269: Each document language may have dif
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Page 272 and 273: help Help is available for the obje
Page 274 and 275: 18.3 User preferences for fonts As
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Example(s): For example, to draw a
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spatial audio), and paragraphs of c
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Value: | | inherit Initial: depen
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Example(s): The following two rules
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far-right Same as ’60deg’. With
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fast Same as 300 words per minute.
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Values have the following meanings:
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290
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SUB { vertical-align: sub } SUP { v
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Dynamic outlines [p. 274] . B.2 Upd
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the native font format on the Amiga
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TrueDoc TrueDoc technology was deve
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Square Cove (4) Obtuse Square Cove
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XHeight Standard/Serifed (4) High/T
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Block Add Block name Unicode range
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This table suggests where such info
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308
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pseudo_page : ’:’ IDENT ; font_
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{num}rad {num}grad {num}ms {num}s {
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[RFC1808] "Relative Uniform Resourc
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[RFC1630] "Universal Resource Ident
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Name ’border-top-width’ [p. 88]
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Name ’list-style-type’ [p. 168]
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Name ’speech-rate’ [p. 285] Val
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Name Values Initial value ’mathli
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’ascent’ (descriptor), 222 aspe
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close-quote, 159, 155 collapsing ma
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font family, 198 font set, 199 font
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definition of, 43 ’letter-spacing
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page model, 175 page selector, 176
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simple selector, 55 ’size’, 177
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valid style sheet, 29 value, 41 ver
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