Contents
Setting font Descriptionsproperties will be among the most common uses of style
sheets. Unfortunately, there exists no well-defined and @font-face 15.3.2 Descriptorsuniversally
accepted taxonomy for Selecting a Font: 'font-family' , 'font-style' , 'font-variant' , 'font-weight' , 'font-stretch'classifying fonts, and 'font-size' 15.3.3 Descriptors forterms that apply to one
font Data Qualification: 'unicode-range' 15.3.4 Descriptor for Numeric Values: 'units-per-em' 15.3.5 Descriptor for Referencing: 'src' 15.3.6 Descriptors for Matching: 'panose-1' , 'stemv' , 'stemh' , 'slope' , 'cap-height' , 'x-height' , 'ascent' , and 'descent' 15.3.7 Descriptors for Synthesis: 'widths' , 'bbox' and 'definition-src' 15.3.8 Descriptorsfamily may not be appropriate for Alignment: 'baseline' , 'centerline' , 'mathline' , and 'topline' 15.3.9 Examples 15.4 Font Characteristics 15.4.1 Introducing Font Characteristics 15.4.2 Full font name 15.4.3 Coordinate units on the em square 15.4.4 Central Baseline 15.4.5 Font Encoding 15.4.6others. E.g. 'italic' is
commonly used to label slanted text, but slanted text may also be
labeled as being Oblique, Slanted, Incline, Cursive or
Kursiv. Therefore it is not a simple problem to map typical
font family name 15.4.7 Glyph widths 15.4.8 Horizontal stem width 15.4.9 Height of uppercase glyphs 15.4.10 Height of lowercase glyphs 15.4.11 Lower Baseline 15.4.12 Mathematical Baseline 15.4.13 Maximal bounding box 15.4.14 Maximum unaccented height 15.4.15 Maximum unaccented depth 15.4.16 Panose-1 number 15.4.17 Range of ISO 10646 characters 15.4.18 Top Baseline 15.4.19 Vertical stem width 15.4.20 Vertical stroke angle 15.5selection properties to a specific font.
15.5.1 Mapping font weight values to font names 15.5.2 ExamplesBecause there is no accepted, universal taxonomy of font
properties, matching 15.1 Introduction When a document's text isof properties to be displayed visually, characters (abstract information elements)font faces must be mapped to abstract glyphs . One or more characters may be depicted by one or more abstract glyphs,done
carefully. The properties are matched in a possibly context-dependent fashion. A glyph iswell-defined order to
insure that the actual artistic representationresults of an abstract glyph, in some typographic style, inthis matching process are as consistent as
possible across UAs (assuming that the formsame library of outlines or bitmaps that may be drawn on the screen or paper. Afont faces is
presented to each of them).
(The above algorithm can be optimized to avoid having to revisit
the font selection mechanism , wherebyCSS 2.1 properties for each character.)
The client's user agent identifies and loadsper-property matching rules from (2) above are as follows:
| Value: | [[ <family-name> | <generic-family> ] [, <family-name>| <generic-family>]* ] | inherit |
| Initial: | depends on user agent |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | as specified |
The new setvalue is a prioritized list of font propertyfamily names and/or generic
family names. Unlike most other CSS properties, values will then be usedare separated
by a comma to select from the font database again.indicate that they are alternatives:
body { font-family: Gill, Helvetica, sans-serif }
Although many fonts provide the result is"missing character" glyph,
typically an increase in regularityopen box, as its name implies this should not be
considered a match
for style sheet authors and implementors, and an increasecharacters that cannot be found in robustness. 15.2.1 Font specification properties CSS2 specifies fonts according to these characteristics: Font familythe font. (It should,
however, be considered a match for U+FFFD, the "missing character"
character's code point).
There are two types of font family specifies which font family is to be used to rendernames:
Style sheet designers are encouraged to offer a generic font family
names include "Helvetica", "New Century Schoolbook", and "Kyokasho ICA L".as a last alternative. Generic font family names are keywords and must NOT restricted to Latin characters.be quoted.
If an unquoted font families mayfamily name contains
parentheses, brackets, and/or braces, they must still be grouped into different categories: those witheither balanced or
without serifs, those whoseescaped per CSS grammar rules. Similarly, quote marks, semicolons,
exclamation marks and commas within unquoted font family names must be escaped.
Font names containing any such characters areor are not proportionally spaced, those that resemble handwriting, those that are fantasy fonts, etc. Font stylewhitespace should be quoted:
body { font-family: "New Century Schoolbook", serif }
<BODY STYLE="font-family: 'My own font', fantasy">
If quoting is omitted, any whitespace characters before and after
the font style specifies whethername are ignored and any sequence of whitespace characters
inside the textfont name is converted to be rendered using a normal, italic, or oblique face. Italic isa more cursive companion facesingle space.
Font family names that happen to be the normal face, but not so cursivesame as to make it a script face. Oblique isa slanted form of the normal face,keyword value (e.g. 'initial', 'inherit', 'default', 'serif', 'sans-serif', 'monospace', 'fantasy', and is more commonly used as a companion face to sans-serif. This definition avoids having'cursive') must be quoted to label slightly slanted normal faces as oblique, or normal Greek facesprevent confusion with the keywords with the same names. UAs must not consider these keywords as italic. Font variantmatching the '<family-name>' type.
| Value: | normal |
| Initial: | |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| | as specified |
The 'font-style' property specifiesselects between normal (sometimes
referred to as "roman" or "upright"), italic and oblique faces within
a prioritized listfont family.
A value of 'normal' selects a font family names and/or generic family names. To deal with the problemthat is classified as 'normal'
in the UA's font database, while 'oblique' selects a singlefont may not contain glyphs to display all the characters in a document, orthat not all fonts are available on all systems, this property allows authors to specifyis
labeled 'oblique'. A list of fonts, allvalue of the same style and size, that are tried in sequence to see if they contain a glyph for a certain character. This list is called'italic' selects a font set . Example(s): For example, textthat contains English words mixed with mathematical symbols may need a font set of two fonts,is labeled
'italic', or, if that is not available, one containing Latin letters and digits,labeled 'oblique'.
The other containing mathematical symbols. Here is an example of afont set suitable for a textthat is expected to contain text with Latin characters, Japanese characters, and mathematical symbols: BODY { font-family: Baskerville, "Heisi Mincho W3", Symbol, serif } The glyphs availablelabeled 'oblique' in the "Baskerville" font (aUA's font that covers only Latin characters)database may
actually have been generated by electronically slanting a normal font.
Fonts with Oblique, Slanted or Incline in their names will
typically be taken from that font, Japanese glyphslabeled 'oblique' in the UA's font database. Fonts with
Italic, Cursive or Kursiv in their names will
typically be taken from "Heisi Mincho W3", andlabeled 'italic'.
h1, h2, h3 { font-style: italic }
h1 em { font-style: normal }
In the mathematical symbol glyphs will come from "Symbol". Any othersexample above, emphasized text within 'H1' will come from the generic font family 'serif'.appear in a
normal face.
| Value: | normal | small-caps | inherit |
| Initial: | normal |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | as specified |
Another type of variation within a font family will be used if one or more ofis the other fontssmall-caps.
In a small-caps font set is unavailable. Although many fonts providethe "missing character" glyph, typically an open box, as its name implies this should not be considered a match except forlower case letters look similar to the
last fontuppercase ones, but in a font set. There are two types of font family names: <family-name>smaller size and with slightly different
proportions. The name'font-variant' property selects that font.
A value of 'normal' selects a font family of choice.that is not a small-caps font,
'small-caps' selects a small-caps font. It is acceptable (but not
required) in the previous example, "Baskerville", "Heisi Mincho W3", and "Symbol" are font families. Font family names containing whitespace should be quoted.CSS 2.1 if quoting is omitted, any whitespace characters before and after the font name are ignored and any sequence of whitespace characters insidethe small-caps font nameis converted toa single space. <generic-family> The following generic families are defined: 'serif', 'sans-serif', 'cursive', 'fantasy', and 'monospace'. Please see the section on generic font families for descriptions of these families. Generic font family names are keywords, and therefore must not be quoted. Authors are encouraged to offercreated by taking a
genericnormal font familyand replacing the lower case letters by scaled uppercase
characters. As a last alternative, for improved robustness. For example: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"> <HTML> <HEAD> <TITLE>Font test</TITLE> <STYLE type="text/css"> BODY { font-family: "new century schoolbook", serif } </STYLE> </HEAD> <BODY> <H1 style="font-family: 'My own font', fantasy">Test</H1> <P>What's up, Doc? </BODY> </HTML> Example(s): The richer selector syntax of CSS2 mayresort, uppercase letters will be used to create language-sensitive typography.as
replacement for example, some Chinese and Japanese characters are unified to have the same Unicode codepoint, although the abstract glyphs are nota small-caps font.
The samefollowing example results in the two languages. *:lang(ja-jp)an 'H3' element in small-caps,
with any emphasized words in oblique, and any emphasized words within
an 'H3' oblique small-caps:
h3 { font: 900 14pt/16pt "Heisei Mincho W9", seriffont-variant: small-caps }
*:lang(zh-tw)em { font: 800 14pt/16.5pt "Li Sung", seriffont-style: oblique }
This selects any element that hasThere may be other variants in the given language - Japanesefont family as well, such as
fonts with old-style numerals, small-caps numerals, condensed or
Traditional Chinese - and requestsexpanded letters, etc. CSS 2.1 has no properties that select those.
Note: insofar as this property causes text to be
transformed to uppercase, the appropriate font. 15.2.3same considerations as for 'text-transform' apply.
| Value: | normal | |
| Initial: | normal |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | see text |
The 'font-style''font-weight' property requests normal (sometimes referred to as "roman" or "upright"), italic, and oblique faces within a font family. Values haveselects the following meanings: normal Specifiesweight of the font. The
values '100' to '900' form an ordered sequence, where each number
indicates a fontweight that is classifiedat least as 'normal' indark as its predecessor. The
UA'skeyword 'normal' is synonymous with '400', and 'bold' is synonymous
with '700'. Keywords other than 'normal' and 'bold' have been shown to
be often confused with font database. oblique Specifiesnames and a numerical scale was therefore
chosen for the 9-value list.
p { font-weight: normal } /* 400 */
h1 { font-weight: 700 } /* bold */
The 'bolder' and 'lighter' values select font weights that is classified as 'oblique' inare
relative to the UA's font database.weight inherited from the parent:
strong { font-weight: bolder }
Child elements inherit the resultant weight, not the keyword value.
Fonts with Oblique, Slanted,(the font data) typically have one or Incline in theirmore properties whose
values are names will typically be labeled 'oblique' inthat are descriptive of the font database."weight" of a font thatfont. There
is labeled 'oblique' in the UA's font database may actually have been generated by electronically slantingno accepted, universal meaning to these weight names. Their primary
role is to distinguish faces of differing darkness within a normal font. italic Specifiessingle
font family. Usage across font families is quite variant; for example,
a font that is classifiedone might think of as 'italic' inbeing bold might be described as
being Regular, Roman, Book, Medium, Semi- or DemiBold,
Bold, or Black, depending on how black the "normal" face
of the UA'sfont database, or, if thatis not available, one labeled 'oblique'. Fonts with Italic, Cursive , or Kursivwithin the design. Because there is no standard usage
of names, the weight property values in their namesCSS 2.1 are given on a numerical
scale in which the value '400' (or 'normal') corresponds to the
"normal" text face for that family. The weight name associated with
that face will typically be labeled 'italic'. Example(s): In this example,Book, Regular, Roman, Normal text in an H1, H2,or
H3 element will be displayed with an italic font. However, emphasized text (EM)sometimes Medium.
The association of other weights within an H1 will appear in a normal face. H1, H2, H3 { font-style: italic } H1 EM { font-style: normal } 'font-variant' Value: normal | small-caps | inherit Initial: normal Applies to: all elements Inherited: yes Percentages: N/A Media: visual Ina small-caps font,family to the glyphs for lowercase letters look similarnumerical
weight values is intended only to preserve the uppercase ones, but in a smaller size and with slightly different proportions.ordering of darkness
within that family. However, the 'font-variant' property requests such a font for bicameral (having two cases, as with Latin script). This property has no visible effect for scripts that are unicameral (having only one case, as with most offollowing heuristics tell how the
world's writing systems). Values haveassignment is done in typical cases:
The inherited value was '900',following two examples show typical mappings.
Assume four weights in which case the resulting weight is also '900'. lighter Specifiesthe next weight that is assigned"Rattlesnake" family, from lightest to
a font that is lighter thandarkest: Regular, Medium, Bold, Heavy.
| Available faces | Assignments | Filling the |
|---|---|---|
| "Rattlesnake Regular" | 400 | 100, 200, 300 |
| "Rattlesnake Medium" | 500 | |
| "Rattlesnake Bold" | 700 | 600 |
| "Rattlesnake Heavy" | 800 | 900 |
Assume six weights in the
next lighter numerical value (and the font remains unchanged), unless"Ice Prawn" family: Book, Medium, Bold, Heavy, Black,
ExtraBlack. Note that in this instance the inheriteduser agent
has decided not to assign a numeric
value was '100', in which caseto "Ice Prawn ExtraBlack".
| Available faces | Assignments | Filling the |
|---|---|---|
| "Ice Prawn Book" | 400 | |
| "Ice Prawn Medium" | 500 | |
| "Ice Prawn Bold" | 700 | 600 |
| "Ice Prawn Heavy" | 800 | |
| "Ice Prawn Black" | 900 | |
| "Ice Prawn ExtraBlack" | (none) |
Since the computed valueintent of the weight. 'font-stretch' Value: normal | wider | narrower | ultra-condensed | extra-condensed | condensed | semi-condensed | semi-expanded | expanded | extra-expanded | ultra-expanded | inherit Initial: normal Applies to: all elements Inherited: yes Percentages: N/A Media: visual The 'font-stretch' property selects a normal, condensed,relative keywords 'bolder' and 'lighter' is
to darken or extendedlighten the face fromwithin the family and because a
font family. Absolute keyword valuesfamily may not have faces aligned with all the following ordering, from narrowestsymbolic weight values,
the matching of 'bolder' is to widest : ultra-condensed extra-condensed condensed semi-condensed normal semi-expanded expanded extra-expanded ultra-expandedthe relative keyword 'wider' setsnext darker face available on the
valueclient within the family and the matching of 'lighter' is to the next
expanded value abovelighter face within the inherited value (while not increasing it above 'ultra-expanded');family. To be precise, the meaning of the
relative keyword 'narrower' setskeywords 'bolder' and 'lighter' is as follows:
There is no guarantee that there will be a darker face for each of the 'font-weight' values; for example, some fonts may have only a normal and a bold face, while others may have eight face weights. There is no guarantee on how a UA will map font faces within a family to weight values. The only guarantee is that a face of a given value will be no less dark than the faces of lighter values.
The computed value of "font-weight" is either:
CSS 2.1 does not specify how the computed value of font-weight is represented internally or externally.
| Value: | <absolute-size> | <relative-size> | <length> | <percentage> | inherit |
| Initial: | medium |
| Applies to: | all elements |
| Inherited: | |
| Percentages: | refer to parent element's font size |
| Media: | visual |
| | absolute length |
The font size ofcorresponds to the font when set solid.em square, a concept used in typography.
Note that certain glyphs may bleed outside their em squares. Values
have the following meanings:
[ xx-small | x-small | small | medium | large | x-large | xx-large ]
On a computer screen aThe following table provides user agent guidelines for the absolute-size
scaling factor of 1.2 is suggested between adjacent indexes; ifand their mapping to HTML heading and absolute font-sizes. The
'medium' fontvalue is 12pt,used as the 'large' font could be 14.4pt. Different media may need different scaling factors. Also,reference middle value. The user agent should take the quality and availability ofmay fine
tune these values for different fonts or different types of display devices.
| CSS absolute-size values | xx-small | x-small | small | medium | large | x-large | xx-large | |
|---|---|---|---|---|---|---|---|---|
| scaling factor | 3/5 | 3/4 | 8/9 | 1 | 6/5 | 3/2 | 2/1 | 3/1 |
| HTML headings | h6 | h5 | h4 | h3 | h2 | h1 | ||
| HTML font sizes | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Different media may need different scaling factors. Also, the UA should take the quality and availability of fonts into account when computing the table. The table may be different from one font family to another.
Note.Note 1. To preserve readability, a UA applying
these guidelines should nevertheless avoid creating font-size resulting
in less than 9 pixels per EM unit on a computer display.
Note 2. In CSS1, the suggested scaling factor between adjacent indexes was 1.5 which user experience proved to be too large. In CSS2, the suggested scaling factor for computer screen between adjacent indexes was 1.2 which still created issues for the small sizes. The new scaling factor varies between each index to provide better readability.
<length> ALength value specifies an absoluteand percentage values should not take the font size (that is independent oftable
into account when calculating the user agent'sfont table).size of the element.
Negative lengthsvalues are illegal. <percentage> A percentage value specifies an absolute font size relativenot allowed.
On all other properties, 'em' and 'ex' length values refer to the
parent element'scomputed font size. Usesize of percentage values, or values in 'em's, leadsthe current element. On the 'font-size' property, these
length units refer to more robust and cascadable style sheets.the actual valuecomputed font size of this property may differ fromthe computed value due a numerical valueparent element.
Note that an application may reinterpret an explicit size,
depending on 'font-size-adjust' andthe unavailability of certaincontext. E.g., inside a VR scene a font sizes. Child elements inherit the computed 'font-size' value (otherwise, the effectmay get a
different size because of 'font-size-adjust' would compound). Example(s):perspective distortion.
Examples:
p { font-size: 16px; }
@media print {
p { font-size: 12pt; }
}
blockquote { font-size: larger }
em { font-size: 150% }
em { font-size: 1.5em }
| Value: | |
| Initial: | see individual properties |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | |
| Media: | visual |
| | see individual properties |
The subjective apparent size and legibility of'font' property is,
except as described below, a font are less dependent on theirshorthand property for
setting
'font-style',
'font-variant',
'font-weight',
'font-size' value than on the value of their 'x-height',
or, more usefully, on the ratio of these two values, called the aspect value (font size divided by x-height). The higher'line-height' and
'font-family' at the aspect value,same
place in the more likely it is that a font at smaller sizes will be legible. Inversely, faces with a lower aspect value will become illegible more rapidly below a given threshold size than faces with a higher aspect value. Straightforward font substitution that relies on font size alone may lead to illegible characters. For example,style
sheet. The popular font Verdana has an aspect value of 0.58; when Verdana's font size 100 units, its x-height is 58 units. For comparison, Times New Roman has an aspect valuesyntax of 0.46. Verdana will therefore tend to remain legible at smaller sizes than Times New Roman. Conversely, Verdana will often look 'too big' if substituted for Times New Roman at a chosen size.this property allows authorsis based on a traditional
typographical shorthand notation to specify an aspect value for an element that will preserve the x-height of theset multiple properties related to
fonts.
All font-related properties are first choice fontreset to their initial values,
including those listed in the substitute font.preceding paragraph.
Then, those properties that are given explicit values have the following meanings: none Do not preserve the font's x-height. <number> Specifies the aspect value.in the
number refers'font' shorthand are set to the aspect value of the first choice font. The scaling factor for available fonts is computed according to the following formula: y(a/a') = c where: y = 'font-size' of first-choice font a' = aspect value of available font c = 'font-size' to apply to available font Example(s): For example, if 14px Verdana (with an aspect value of 0.58) was unavailable and an available font had an aspect value of 0.46, the font-size of the substitute would be 14 * (0.58/0.46) = 17.65px. Font size adjustments take place when computing the actual value of 'font-size' . Since inheritance is based on the computed value , child elements will inherit unadjusted values. The first image below shows several typefaces rasterized at a common font size (11pt. at 72 ppi), together with their aspect values. Note that faces with higher aspect values appear larger than those with lower. Faces with very low aspect values are illegible at the size shown. The next image shows the results of 'font-size-adjust' where Verdana has been taken as the"first choice", together with the scaling factor applied. As adjusted, the apparent sizes are nearly linear across faces, though the actual (em) sizes vary by more than 100%. Note that 'font-size-adjust' tends to stabilize the horizontal metrics of lines, as well. 15.2.5 Shorthand font property : the 'font' property 'font' Value: [ [ <'font-style'> || <'font-variant'> || <'font-weight'> ]? <'font-size'> [ / <'line-height'> ]? <'font-family'> ] | caption | icon | menu | message-box | small-caption | status-bar | inherit Initial: see individual properties Applies to: all elements Inherited: yes Percentages: allowed on 'font-size' and 'line-height' Media: visual The 'font' property is, except as described below , a shorthand property for setting 'font-style' , 'font-variant' , 'font-weight' , 'font-size' , 'line-height' , and 'font-family' , at the same place in the style sheet. The syntax of this property is based on a traditional typographical shorthand notation to set multiple properties related to fonts. All font-related properties are first reset to their initial values, including those listed in the preceding paragraph plus 'font-stretch' and 'font-size-adjust' . Then, those properties that are given explicit values in the 'font' shorthand are set to those values. For a definitionthose values.
For a definition of allowed and initial values, see the previously defined properties.
Forreasonsofbackwardscompatibility,itisnotpossibletoset'font-stretch'and'font-size-adjust'tootherthantheirinitialvaluesusingthe'font'shorthandproperty;instead,settheindividualproperties.Example(s):p { font:12pt/14pt12px/14px sans-serif } p { font: 80% sans-serif } p { font: x-large/110% "New Century Schoolbook", serif } p { font: bold italic large Palatino, serif } p { font: normal small-caps120%/120%fantasy}P{font:oblique12pt"HelveticaNue",serif;font-stretch:condensed}Inthesecondrule,thefontsizepercentagevalue('80%')referstothefontsizeoftheparentelement.Inthethirdrule,thelineheightpercentage('110%')referstothefontsizeoftheelementitself.Thefirstthreerulesdonotspecifythe'font-variant'and'font-weight'explicitly,sothesepropertiesreceivetheirinitialvalues('normal').Noticethatthefontfamilyname"newcenturyschoolbook",whichcontainsspaces,isenclosedinquotes.Thefourthrulesetsthe'font-weight'to'bold',the'font-style'to'italic',andimplicitlysets'font-variant'to'normal'.Thefifthrulesetsthe'font-variant'('small-caps'),the'font-size'(120%oftheparent'sfontsize),the'line-height'(120%ofthefontsize)andthe'font-family'('fantasy').Itfollowsthatthekeyword'normal'appliestothetworemainingproperties:'font-style'and'font-weight'.Thesixthrulesetsthe'font-style','font-size',and'font-family',theotherfontpropertiesbeingsettotheirinitialvalues.Itthensets'font-stretch'to'condensed'sincethatpropertycannotbesettothatvalueusingthe'font'shorthandproperty.Thefollowingvaluesrefertosystemfonts:captionThefontusedforcaptionedcontrols(e.g.,buttons,drop-downs,etc.).iconThefontusedtolabelicons.menuThefontusedinmenus(e.g.,dropdownmenusandmenulists).message-boxThefontusedindialogboxes.small-captionThefontusedforlabelingsmallcontrols.status-barThefontusedinwindowstatusbars.Systemfontsmayonlybesetasawhole;thatis,thefontfamily,size,weight,style,etc.areallsetatthesametime.Thesevaluesmaythenbealteredindividuallyifdesired.Ifnofontwiththeindicatedcharacteristicsexistsonagivenplatform,theuseragentshouldeitherintelligentlysubstitute(e.g.,asmallerversionofthe'caption'fontmightbeusedforthe'smallcaption'font),orsubstituteauseragentdefaultfont.Asforregularfonts,if,forasystemfont,anyoftheindividualpropertiesarenotpartoftheoperatingsystem'savailableuserpreferences,thosepropertiesshouldbesettotheirinitialvalues.Thatiswhythispropertyis"almost"ashorthandproperty:systemfontscanonlybespecifiedwiththisproperty,notwith'font-family'itself,so'font'allowsauthorstodomorethanthesumofitssubproperties.However,theindividualpropertiessuchas'font-weight'arestillgivenvaluestakenfromthesystemfont,whichcanbeindependentlyvaried.Example(s):BUTTON{font:300italic1.3em/1.7em"FBArmada",sans-serif}BUTTONP{font:menu}BUTTONPEM{font-weight:bolder}Ifthefontusedfordropdownmenusonaparticularsystemhappenedtobe,forexample,9-pointCharcoal,withaweightof600,thenPelementsthatweredescendantsofBUTTONwouldbedisplayedasifthisrulewereineffect:BUTTONP{font:6009ptCharcoal}Becausethe'font'shorthandresetstoitsinitialvalueanypropertynotexplicitlygivenavalue,thishasthesameeffectasthisdeclaration:BUTTONP{font-style:normal;font-variant:normal;font-weight:600;font-size:9pt;line-height:normal;font-family:Charcoal}15.2.6GenericfontfamiliesGenericfontfamiliesareafallbackmechanism,ameansofpreservingsomeofthestylesheetauthor'sintentintheworstcasewhennoneofthespecifiedfontscanbeselected.Foroptimumtypographiccontrol,particularnamedfontsshouldbeusedinstylesheets.AllfivegenericfontfamiliesaredefinedtoexistinallCSSimplementations(theyneednotnecessarilymaptofivedistinctactualfonts).Useragentsshouldprovidereasonabledefaultchoicesforthegenericfontfamilies,whichexpressthecharacteristicsofeachfamilyaswellaspossiblewithinthelimitsallowedbytheunderlyingtechnology.Useragentsareencouragedtoallowuserstoselectalternativechoicesforthegenericfonts.serifGlyphsofseriffonts,asthetermisusedinCSS,havefinishingstrokes,flaredortaperingends,orhaveactualserifedendings(includingslabserifs).Seriffontsaretypicallyproportionately-spaced.Theyoftendisplayagreatervariationbetweenthickandthinstrokesthanfontsfromthe'sans-serif'genericfontfamily.CSSusestheterm'serif'toapplytoafontforanyscript,althoughothernamesmaybemorefamiliarforparticularscripts,suchasMincho(Japanese),SungorSong(Chinese),TotumorKodig(Korean).Anyfontthatissodescribedmaybeusedtorepresentthegeneric'serif'family.Examplesoffontsthatfitthisdescriptioninclude:LatinfontsTimesNewRoman,Bodoni,Garamond,MinionWeb,ITCStoneSerif,MSGeorgia,BitstreamCyberbitGreekfontsBitstreamCyberbitCyrillicfontsAdobeMinionCyrillic,ExcelciorCyrillicUpright,MonotypeAlbion70,BitstreamCyberbit,ERBukinstHebrewfontsNewPeninim,Raanana,BitstreamCyberbitJapanesefontsRyuminLight-KL,KyokashoICA,FutoMinA101ArabicfontsBitstreamCyberbitCherokeefontsLoCiceroCherokeesans-serifGlyphsinsans-seriffonts,asthetermisusedinCSS,havestrokeendingsthatareplain--withoutanyflaring,crossstroke,orotherornamentation.Sans-seriffontsaretypicallyproportionately-spaced.Theyoftenhavelittlevariationbetweenthickandthinstrokes,comparedtofontsfromthe'serif'family.CSSusestheterm'sans-serif'toapplytoafontforanyscript,althoughothernamesmaybemorefamiliarforparticularscripts,suchasGothic(Japanese),Kai(Chinese),orPathang(Korean).Anyfontthatissodescribedmaybeusedtorepresentthegeneric'sans-serif'family.Examplesoffontsthatfitthisdescriptioninclude:LatinfontsMSTrebuchet,ITCAvantGardeGothic,MSArial,MSVerdana,Univers,Futura,ITCStoneSans,GillSans,AkzidenzGrotesk,HelveticaGreekfontsAttika,TypikoNewEra,MSTahoma,MonotypeGillSans571,HelveticaGreekCyrillicfontsHelveticaCyrillic,ERUnivers,LucidaSansUnicode,BastionHebrewfontsArialHebrew,MSTahomaJapanesefontsShinGo,HeiseiKakuGothicW5ArabicfontsMSTahomacursiveGlyphsincursivefonts,asthetermisusedinCSS,generallyhaveeitherjoiningstrokesorothercursivecharacteristicsbeyondthoseofitalictypefaces.Theglyphsarepartiallyorcompletelyconnected,andtheresultlooksmorelikehandwrittenpenorbrushwritingthanprintedletterwork.Fontsforsomescripts,suchasArabic,arealmostalwayscursive.CSSusestheterm'cursive'toapplytoafontforanyscript,althoughothernamessuchasChancery,Brush,SwingandScriptarealsousedinfontnames.Examplesoffontsthatfitthisdescriptioninclude:LatinfontsCaflischScript,AdobePoetica,Sanvito,ExPonto,SnellRoundhand,Zapf-ChanceryCyrillicfontsERArchitektHebrewfontsCorsivaArabicfontsDecoTypeNaskh,MonotypeUrdu507fantasyFantasyfonts,asusedinCSS,areprimarilydecorativewhilestillcontainingrepresentationsofcharacters(asopposedtoPiorPicturefonts,whichdonotrepresentcharacters).Examplesinclude:LatinfontsAlphaGeometrique,Critter,Cottonwood,FBReactor,StudzmonospaceThesolecriterionofamonospacefontisthatallglyphshavethesamefixedwidth.(Thiscanmakesomescripts,suchasArabic,lookmostpeculiar.)Theeffectissimilartoamanualtypewriter,andisoftenusedtosetsamplesofcomputercode.Examplesoffontswhichfitthisdescriptioninclude:LatinfontsCourier,MSCourierNew,Prestige,EversonMonoGreekFontsMSCourierNew,EversonMonoCyrillicfontsERKurier,EversonMonoJapanesefontsOsakaMonospacedCherokeefontsEversonMono15.3FontselectionThesecondphaseoftheCSS2fontmechanismconcernstheuseragent'sselectionofafontbasedonauthor-specifiedfontproperties,availablefonts,etc.Thedetailsofthefontmatchingalgorithmareprovidedbelow.Therearefourpossiblefontselectionactions:namematching,intelligentmatching,synthesis,anddownload.fontnamematchingInthiscase,theuseragentusesanexisting,accessiblefontthathasthesamefamilynameastherequestedfont.(Notethattheappearanceandthemetricsmightnotnecessarilymatch,ifthefontthatthedocumentauthorusedandthefontontheclientsystemarefromdifferentfoundries).ThematchinginformationisrestrictedtotheCSSfontproperties,includingthefamilyname.ThisistheonlymethodusedbyCSS1.intelligentfontmatchingInthiscase,theuseragentusesanexisting,accessiblefontthatistheclosestmatchinappearancetotherequestedfont.(Notethatthemetricsmightnotmatchexactly).Thematchinginformationincludesinformationaboutthekindoffont(textorsymbol),natureofserifs,weight,capheight,xheight,ascent,descent,slant,etc.fontsynthesisInthiscase,theuseragentcreatesafontthatisnotonlyaclosematchinappearance,butalsomatchesthemetricsoftherequestedfont.Thesynthesizinginformationincludesthematchinginformationandtypicallyrequiresmoreaccuratevaluesfortheparametersthanareusedforsomematchingschemes.Inparticular,synthesisrequiresaccuratewidthmetricsandcharactertoglyphsubstitutionandpositioninformationifallthelayoutcharacteristicsofthespecifiedfontaretobepreserved.fontdownloadFinally,theuseragentmayretrieveafontovertheWeb.Thisissimilartotheprocessoffetchingimages,sounds,orappletsovertheWebfordisplayinthecurrentdocument,andlikewisecancausesomedelaybeforethepagecanbedisplayed.Progressiverenderingisacombinationofdownloadandoneoftheothermethods;itprovidesatemporarysubstitutefont(usingnamematching,intelligentmatching,orsynthesis)toallowcontenttobereadwhiletherequestedfontdownloads.Oncetherealfonthasbeensuccessfullydownloaded,itreplacesthetemporaryfont,hopefullywithouttheneedtoreflow.Note.Progressiverenderingrequiresmetricinformationaboutthefontinordertoavoidre-layoutofthecontentwhentheactualfonthasbeenloadedandrendered.Thismetricinformationissufficientlyverbosethatitshouldonlybespecifiedatmostonceperfontinadocument.15.3.1FontDescriptionsand@font-faceThefontdescriptionprovidesthebridgebetweenanauthor'sfontspecificationandthefontdata,whichisthedataneededtoformattextandtorendertheabstractglyphstowhichthecharactersmap-theactualscalableoutlinesorbitmaps.Fontsarereferencedbystylesheetproperties.Thefontdescriptionisaddedtothefontdatabaseandthenusedtoselecttherelevantfontdata.ThefontdescriptioncontainsdescriptorssuchasthelocationofthefontdataontheWeb,andcharacterizationsofthatfontdata.Thefontdescriptorsarealsoneededtomatchthestylesheetfontpropertiestoparticularfontdata.Thelevelofdetailofafontdescriptioncanvaryfromjustthenameofthefontuptoalistofglyphwidths.Fontdescriptorsmaybeclassifiedintothreetypes:thosethatprovidethelinkbetweentheCSSusageofthefontandthefontdescription(thesehavethesamenamesasthecorrespondingCSSfontproperties),theURIforthelocationofthefontdata,thosethatfurthercharacterizethefont,toprovidealinkbetweenthefontdescriptionandthefontdata.Allfontdescriptionsarespecifiedviaa@font-faceat-rule.Thegeneralformis:@font-face{<font-description>}wherethe<font-description>hastheform:descriptor:value;descriptor:value;[...]descriptor:value;Each@font-facerulespecifiesavalueforeveryfontdescriptor,eitherimplicitlyorexplicitly.Thosenotgivenexplicitvaluesintheruletaketheinitialvaluelistedwitheachdescriptorinthisspecification.Thesedescriptorsapplysolelywithinthecontextofthe@font-faceruleinwhichtheyaredefined,anddonotapplytodocumentlanguageelements.Thus,thereisnonotionofwhichelementsthedescriptorsapplyto,orwhetherthevaluesareinheritedbychildelements.Theavailablefontdescriptorsaredescribedinlatersectionsofthisspecification.Forexample,herethefont'RobsonCeltic'isdefinedandreferencedinastylesheetcontainedinanHTMLdocument.<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.0//EN"><HTML><HEAD><TITLE>Fonttest</TITLE><STYLETYPE="text/css"MEDIA="screen,print">@font-face{font-family:"RobsonCeltic";src:url("http://site/fonts/rob-celt")}H1{font-family:"RobsonCeltic",serif}</STYLE></HEAD><BODY><H1>ThisheadingisdisplayedusingRobsonCeltic</H1></BODY></HTML>Thestylesheet(intheSTYLEelement)containsaCSSrulethatsetsallH1elementstousethe'RobsonCeltic'fontfamily.ACSS1implementationwillsearchtheclientforafontwhosefamilynameandotherpropertiesmatch'RobsonCeltic'and,ifitfailstofindit,willusetheUA-specificfallbackseriffont(whichisdefinedtoexist).AuseragentimplementingCSS2willfirstexamine@font-facerulesinsearchofafontdescriptiondefining'RobsonCeltic'.Thisexamplecontainsarulethatmatches.Althoughthisruledoesn'tcontainmuchfontdata,itdoeshaveaURIwherethefontcanberetrievedforrenderingthisdocument.Downloadedfontsshouldnotbemadeavailabletootherapplications.Ifnomatching@font-faceisfound,theuseragentwillattemptthesamematchasauseragentimplementingCSS1.Notethatifthefont'RobsonCeltic'hadbeeninstalledontheclientsystem,thiswouldhavecausedtheUAtoaddanentryinthefontdatabasefortheinstalledcopyasdescribedinthesectiononthefontmatchingalgorithm.Theinstalledcopywouldhavebeenmatchedbeforethedownloadablefontintheexampleabove.CSS1implementations,whichdonotunderstandthe@font-facerule,willencountertheopeningcurlybracketsandwillignoreforwarduntilthematchingclosingcurlybrackets.Thisat-ruleconformswiththeforward-compatibleparsingrequirementofCSS.Parsersmayignoretheseruleswithouterror.Havingthefontdescriptorsseparatefromthefontdatahasabenefitbeyondbeingabletodofontselectionand/orsubstitution.Thedataprotectionandreplicationrestrictionsonthefontdescriptorsmaybemuchweakerthanonthefullfontdata.Thus,itmaybepossibletoinstallthefontdefinitionlocally,oratleasttohaveitinalocalcacheifitoccursinacommonlyreferencedstylesheet;thiswouldnotrequireaccessingthefullfontdefinitionovertheWebmorethanoncepernamedfont.Ifafontdescriptorisduplicated,thelastoccurringdescriptorwinsandtherestmustbeignored.Also,anydescriptorsthatarenotrecognizedorusefultotheuseragentmustbeignored.FutureversionsofCSSmayallowadditionaldescriptorsforthepurposeofbetterfontsubstitution,matching,orsynthesis.15.3.2DescriptorsforSelectingaFont:'font-family','font-style','font-variant','font-weight','font-stretch'and'font-size'ThefollowingdescriptorshavethesamenamesasthecorrespondingCSS2fontproperties,andtakeasinglevalueorcomma-separatedlistofvalues.Thevalueswithinthatlistare,exceptasexplicitlynoted,thesameasthoseforthecorrespondingCSS2property.Ifthereisasinglevalue,thatisthevaluethatmustbematched.Ifthereisalist,anylistitemconstitutesamatch.Ifthedescriptorisomittedfromthe@font-face,theinitialvalueforthedescriptorisused.'font-family'(Descriptor)Value:[<family-name>|<generic-family>][,[<family-name>|<generic-family>]]*Initial:dependsonuseragentMedia:visualThisisthedescriptorforthefontfamilynameofafontandtakesthesamevaluesasthe'font-family'property.'font-style'(Descriptor)Value:all|[normal|italic|oblique][,[normal|italic|oblique]]*Initial:allMedia:visualThisisthedescriptorforthestyleofafontandtakesthesamevaluesasthe'font-style'property,exceptthatacomma-separatedlistispermitted.'font-variant'(Descriptor)Value:[normal|small-caps][,[normal|small-caps]]*Initial:normalMedia:visualThisistheCSSindicationofwhetherthisfaceisthesmall-capsvariantofafont.Ittakesthesamevaluesasthe'font-variant'propertyexceptthatacomma-separatedlistispermitted.Note.Cyrillicpryamoĭfacesmaybelabeledwitha'font-variant'ofsmall-caps,whichwillgivebetterconsistencywithLatinfaces(andthecompanionkursivfacelabeledwith'font-style'italicforthesamereason).'font-weight'(Descriptor)Value:all|[normal|bold|100|200|300|400|500|600|700|800|900][,[normal|bold|100|200|300|400|500|600|700|800|900]]*Initial:allMedia:visualThisisthedescriptorfortheweightofafacerelativetoothersinthesamefontfamily.Ittakesthesamevaluesasthe'font-weight'propertywiththreeexceptions:relativekeywords(bolder,lighter)arenotpermitted.acomma-separatedlistofvaluesispermitted,forfontsthatcontainmultipleweights.anadditionalkeyword,'all'ispermitted,whichmeansthatthefontwillmatchforallpossibleweights;eitherbecauseitcontainsmultipleweights,orbecausethatfaceonlyhasasingleweight.'font-stretch'(Descriptor)Value:all|[normal|ultra-condensed|extra-condensed|condensed|semi-condensed|semi-expanded|expanded|extra-expanded|ultra-expanded][,[normal|ultra-condensed|extra-condensed|condensed|semi-condensed|semi-expanded|expanded|extra-expanded|ultra-expanded]]*Initial:normalMedia:visualThisistheCSSindicationofthecondensedorexpandednatureofthefacerelativetoothersinthesamefontfamily.Ittakesthesamevaluesasthe'font-stretch'propertyexceptthat:relativekeywords(wider,narrower)arenotpermittedacomma-separatedlistispermittedThekeyword'all'ispermitted'font-size'(Descriptor)Value:all|<length>[,<length>]*Initial:allMedia:visualThisisthedescriptorforthesizesprovidedbythisfont.Onlyabsolutelengthunitsarepermitted,incontrasttothe'font-size'property,whichallowsbothrelativeandabsolutelengthsandsizes.Acomma-separatedlistofabsolutelengthsispermitted.Theinitialvalueof'all'issuitableformostscalablefonts,sothisdescriptorisprimarilyforuseinan@font-faceforbitmapfonts,orscalablefontsdesignedtoberasterisedatarestrictedrangeoffontsizes.15.3.3DescriptorsforFontDataQualification:'unicode-range'Thefollowingdescriptorisoptionalwithinafontdefinition,butisusedtoavoidcheckingordownloadingafontthatdoesnothavesufficientglyphstorenderaparticularcharacter.'unicode-range'(Descriptor)Value:<urange>[,<urange>]*Initial:U+0-7FFFFFFFMedia:visualThisisthedescriptorfortherangeofISO10646characterscoveredbythefont.Thevaluesof<urange>areexpressedusinghexadecimalnumbersprefixedby"U+",correspondingtocharactercodepositionsinISO10646([ISO10646]).Forexample,U+05D1istheISO10646character'Hebrewletterbet'.ForvaluesoutsidetheBasicMultilingualPlane(BMP),additionalleadingdigitscorrespondingtotheplanenumberareadded,alsoinhexadecimal,likethis:U+A1234whichisthecharacteronPlane10athexadecimalcodeposition1234.AtthetimeofwritingnocharactershadbeenassignedoutsidetheBMP.Leadingzeros(forexample,0000004D)arevalid,butnotrequired.TheinitialvalueofthisdescriptorcoversnotonlytheentireBasicMultilingualPlane(BMP),whichwouldbeexpressedasU+0-FFFF,butalsothewholerepertoireofISO10646.Thus,theinitialvaluesaysthatthefontmayhaveglyphsforcharactersanywhereinISO10646.Specifyingavaluefor'unicode-range'providesinformationtomakesearchingefficient,bydeclaringaconstrainedrangeinwhichthefontmayhaveglyphsforcharacters.Thefontneednotbesearchedforcharactersoutsidethisrange.Valuesmaybewrittenwithanynumberofdigits.Forsinglenumbers,thecharacter'?'isassumedtomean'anyvalue'whichcreatesarangeofcharacterpositions.Thus,usingasinglenumber:unicode-range:U+20A7nowildcards-itindicatesasinglecharacterposition(theSpanishpesetacurrencysymbol)unicode-range:U+215?onewildcard,coverstherange2150to215F(thefractions)unicode-range:U+00??twowildcards,coverstherange0000to00FF(Latin-1)unicode-range:U+E??twowildcards,covers0E00to0EFF(theLaoscript)Apairofnumbersinthisformatcanbecombinedwiththedashcharactertoindicatelargerranges.Forexample:unicode-range:U+AC00-D7FFtherangeisAC00toD7FF(theHangulSyllablesarea)Multiple,discontinuousrangescanbespecified,separatedbyacomma.Aswithothercomma-separatedlistsinCSS,anywhitespacebeforeorafterthecommaisignored.Forexample:unicode-range:U+370-3FF,U+1F??Thiscoverstherange0370to03FF(ModernGreek)plus1F00to1FFF(AncientpolytonicGreek).unicode-range:U+3000-303F,U+3100-312F,U+32??,U+33??,U+4E00-9FFF,U+F9000-FAFF,U+FE30-FE4FSomethingofaworstcaseintermsofverbosity,thisverypreciselyindicatesthatthis(extremelylarge)fontcontainsonlyChinesecharactersfromISO10646,withoutincludinganycharactersthatareuniquelyJapaneseorKorean.Therangeis3000to303F(CJKsymbolsandpunctuation)plus3100to312F(Bopomofo)plus3200to32FF(enclosedCJKlettersandmonths)plus3300to33FF(CJKcompatibilityzone)plus4E00to9FFF(CJKunifiedIdeographs)plusF900toFAFF(CJKcompatibilityideographs)plusFE30toFE4F(CJKcompatibilityforms).AmorelikelyrepresentationforatypicalChinesefontwouldbe:unicode-range:U+3000-33FF,U+4E00-9FFFunicode-range:U+11E00-121FFThisfontcoversaproposedregistrationforAztecpictograms,coveringtherange1E00to21FFinplane1.unicode-range:U+1A00-1A1FThisfontcoversaproposedregistrationforIrishOghamcoveringtherange1A00to1A1F15.3.4DescriptorforNumericValues:'units-per-em'Thefollowingdescriptorspecifiesthenumberof"units"perem;theseunitsmaybeusedbyseveralotherdescriptorstoexpressvariouslengths,so'units-per-em'isrequiredifotherdescriptorsdependonit.'units-per-em'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthenumberofthecoordinateunitsontheemsquare,thesizeofthedesigngridonwhichglyphsarelaidout.15.3.5DescriptorforReferencing:'src'Thisdescriptorisrequiredforreferencingactualfontdata,whetherdownloadableorlocallyinstalled.'src'(Descriptor)Value:[<uri>[format(<string>[,<string>]*)]|<font-face-name>][,<uri>[format(<string>[,<string>]*)]|<font-face-name>]*Initial:undefinedMedia:visualThisisaprioritized,comma-separatedlistofexternalreferencesand/orlocallyinstalledfontfacenames.TheexternalreferencepointstothefontdataontheWeb.ThisisrequirediftheWebFontistobedownloaded.Thefontresourcemaybeasubsetofthesourcefont,forexampleitmaycontainonlytheglyphsneededforthecurrentpageorforasetofpages.TheexternalreferenceconsistsofaURI,followedbyanoptionalhintregardingtheformatoffontresourcetobefoundatthatURI,andthisinformationshouldbeusedbyclientstoavoidfollowinglinkstofontsinformatstheyareunabletouse.Aswithanyhypertextreference,theremaybeotherformatsavailable,buttheclienthasabetterideaofwhatislikelytobethere,inamorerobustwaythantryingtoparsefilenameextensionsinURIs.Theformathintcontainsacomma-separatedlistofformatstringsthatdenotewell-knownfontformats.Theuseragentwillrecognizethenameoffontformatsthatitsupports,andwillavoiddownloadingfontsinformatsthatitdoesnotrecognize.Aninitiallistofformatstringsdefinedbythisspecificationandrepresentingformatslikelytobeusedbyimplementationsonvariousplatformsis:StringFontFormatExamplesofcommonextensions"truedoc-pfr"TrueDoc™PortableFontResource.pfr"embedded-opentype"EmbeddedOpenType.eot"type-1"PostScript™Type1.pfb,.pfa"truetype"TrueType.ttf"opentype"OpenType,includingTrueTypeOpen.ttf"truetype-gx"TrueTypewithGXextensions"speedo"Speedo"intellifont"IntellifontAswithotherURIsinCSS,theURImaybepartial,inwhichcaseitisresolvedrelativetothelocationofthestylesheetcontainingthe@font-face.Thelocally-installed<font-face-name>isthefullfontnameofalocallyinstalledfont.Thefullfontnameisthenameofthefontasreportedbytheoperatingsystemandisthenamemostlikelytobeusedinreaderstylesheets,browserdefaultstylesheetsorpossiblyauthorstylesheetsonanintranet.Adornmentssuchasbold,italic,andunderlineareoftenusedtodifferentiatefaceswithinafontfamily.Formoreinformationaboutfullfontnamespleaseconsultthenotesbelow.Thenotationfora<font-face-name>isthefullfontname,whichmustbequotedsinceitmaycontainanycharacter,includingspacesandpunctuation,andalsomustbeenclosedin"local("and")".Example(s):src:url("http://foo/bar")afullURIandnoinformationaboutthefontformat(s)availabletheresrc:local("BTCentury751No.2SemiBoldItalic")referencesaparticularfaceofalocallyinstalledfontsrc:url("../fonts/bar")format("truedoc-pfr")apartialURIwhichhasafontavailableinTrueDocformatsrc:url("http://cgi-bin/bar?stuff")format("opentype","intellifont")afullURI,inthiscasetoascript,whichcangeneratetwodifferentformats-OpenTypeandIntellifontsrc:local("T-26TypekaMix"),url("http://site/magda-extra")format("type-1")twoalternativesaregiven,firstlyalocallyinstalledfontandsecondlyadownloadablefontavailableinType1format.Accesstolocallyinstalledfontsisviathe<font-face-name>.Thefontfacenameisnottrulyunique,norisittrulyplatformorfontformatindependent,butatthemomentitisthebestwaytoidentifylocallyinstalledfontdata.Theuseofthefontfacenamecanbemademoreaccuratebyprovidinganindicationoftheglyphcomplementrequired.ThismaybedonebyindicatingtherangeofISO10646characterpositionsforwhichthefontprovidessomeglyphs(see'unicode-range').15.3.6DescriptorsforMatching:'panose-1','stemv','stemh','slope','cap-height','x-height','ascent',and'descent'ThesedescriptorsareoptionalforaCSS2definition,butmaybeusedifintelligentfontmatchingorfontsizeadjustmentisdesiredbytheauthor.'panose-1'(Descriptor)Value:[<integer>]{10}Initial:0000000000Media:visualThisisthedescriptorforthePanose-1numberandconsistsoftendecimalintegers,separatedbywhitespace.Acomma-separatedlistisnotpermittedforthisdescriptor,becausethePanose-1systemcanindicatethatarangeofvaluesarematched.Theinitialvalueiszero,whichmeans"any",foreachPANOSEdigit;allfontswillmatchthePanosenumberifthisvalueisused.UseofthePanose-1descriptorisstronglyrecommendedforlatinfonts.Forfurtherdetails,seeAppendixC.'stemv'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorfortheverticalstemwidthofthefont.Ifthevalueisundefined,thedescriptorisnotusedformatching.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.'stemh'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthehorizontalstemwidthofthefont.Ifthevalueisundefined,thedescriptorisnotusedformatching.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.'slope'(Descriptor)Value:<number>Initial:0Media:visualThisisthedescriptorfortheverticalstrokeangleofthefont.'cap-height'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthenumberoftheheightofuppercaseglyphsofthefont.Ifthevalueisundefined,thedescriptorisnotusedformatching.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.'x-height'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorfortheheightoflowercaseglyphsofthefont.Ifthevalueisundefined,thedescriptorisnotusedformatching.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.Thisdescriptorcanbeveryusefulwhenusingthe'font-size-adjust'property,becausecomputationofthezvalueofcandidatefontsrequiresboththefontsizeandthex-height;itisthereforerecommendedtoincludethisdescriptor.'ascent'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthemaximumunaccentedheightofthefont.Ifthevalueisundefined,thedescriptorisnotusedformatching.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.'descent'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorfortheMaximumunaccenteddepthofthefont.Ifthevalueisundefined,thedescriptorisnotusedformatching.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.15.3.7DescriptorsforSynthesis:'widths','bbox'and'definition-src'Synthesizingafontmeans,atminimum,matchingthewidthmetricsofthespecifiedfont.Therefore,forsynthesis,thismetricinformationmustbeavailable.Similarly,progressiverenderingrequireswidthmetricsinordertoavoidreflowofthecontentwhentheactualfonthasbeenloaded.AlthoughthefollowingdescriptorsareoptionalforaCSS2definition,somearerequiredifsynthesizing(orreflow-freeprogressiverendering)isdesiredbytheauthor.Shouldtheactualfontbecomeavailable,thesubstituteshouldbereplacedbytheactualfont.Anyofthesedescriptorsthatarepresentwillbeusedtoprovideabetterorfasterapproximationoftheintendedfont.Ofthesedescriptors,themostimportantarethe'widths'descriptorand'bbox'whichareusedtopreventtextreflowshouldtheactualfontbecomeavailable.Inaddition,thedescriptorsinthesetofdescriptorsusedformatchingcanbeusedtoprovideabettersynthesisoftheactualfontappearance.'widths'(Descriptor)Value:[<urange>]?[<number>]+[,[<urange>]?<number>]+]Initial:undefinedMedia:visualThisisthedescriptorfortheglyphwidths.Thevalueisacomma-separatedlistof<urange>valueseachfollowedbyoneormoreglyphwidths.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.Ifthe<urange>isomitted,arangeofU+0-7FFFFFFFisassumedwhichcoversallcharactersandtheirglyphs.Ifnotenoughglyphwidthsaregiven,thelastinthelistisreplicatedtocoverthaturange.Iftoomanywidthsareprovided,theextrasareignored.Example(s):Forexample:widths:U+4E00-4E1F173618741692widths:U+1A??1490,U+215?1473183819271684135617921815184818701492171517451584199219781770Inthefirstexamplearangeof32charactersisgiven,from4E00to4E1F.Theglyphcorrespondingtothefirstcharacter(4E00)hasawidthof1736,thesecondhasawidthof1874andthethird,1692.Becausenotenoughwidthshavebeenprovided,thelastwidthreplicatestocovertherestofthespecifiedrange.Thesecondexamplesetsasinglewidth,1490,foranentirerangeof256glyphsandthenexplicitwidthsforarangeof16glyphs.Thisdescriptorcannotdescribemultipleglyphscorrespondingtoasinglecharacter,orligaturesofmultiplecharacters.Thus,thisdescriptorcanonlybeusedforscriptsthatdonothavecontextualformsormandatoryligatures.Itisneverthelessusefulinthosesituations.Scriptsthatrequireaone-to-manyormany-to-manymappingofcharacterstoglyphscannotatpresentusethisdescriptortoenablefontsynthesisalthoughtheycanstillusefontdownloadingorintelligentmatching.'bbox'(Descriptor)Value:<number>,<number>,<number>,<number>Initial:undefinedMedia:visualThisisthedescriptorforthemaximalboundingboxofthefont.Thevalueisacomma-separatedlistofexactlyfournumbersspecifying,inorder,thelowerleftx,lowerlefty,upperrightx,andupperrightyoftheboundingboxforthecompletefont.'definition-src'(Descriptor)Value:<uri>Initial:undefinedMedia:visualThefontdescriptorsmayeitherbewithinthefontdefinitioninthestylesheet,ormaybeprovidedwithinaseparatefontdefinitionresourceidentifiedbyaURI.Thelatterapproachcanreducenetworktrafficwhenmultiplestylesheetsreferencethesamefonts.15.3.8DescriptorsforAlignment:'baseline','centerline','mathline',and'topline'Theseoptionaldescriptorsareusedtoalignrunsofdifferentscriptswithoneanother.'baseline'(Descriptor)Value:<number>Initial:0Media:visualThisisthedescriptorforthelowerbaselineofafont.Ifthisdescriptorisgivenanon-default(non-zero)value,the'units-per-em'descriptormustalsobeused.'centerline'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthecentralbaselineofafont.Ifthevalueisundefined,theUAmayemployvariousheuristicssuchasthemidpointoftheascentanddescentvalues.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.'mathline'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthemathematicalbaselineofafont.Ifundefined,theUAmayusethecenterbaseline.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.'topline'(Descriptor)Value:<number>Initial:undefinedMedia:visualThisisthedescriptorforthetopbaselineofafont.Ifundefined,theUAmayuseanapproximatevaluesuchastheascent.Ifthisdescriptorisused,the'units-per-em'descriptormustalsobeused.15.3.9ExamplesExample(s):Giventhefollowinglistoffonts:Swiss721lightlight&lightitalicSwiss721roman,bold,italic,bolditalicSwiss721mediummedium&mediumitalicSwiss721heavyheavy&heavyitalicSwiss721blackblack,blackitalic,&black#2Swiss721Condensedroman,bold,italic,bolditalicSwiss721Expandedroman,bold,italic,bolditalicThefollowingfontdescriptionscouldbeusedtomakethemavailablefordownload.@font-face{font-family:"Swiss721";src:url("swiss721lt.pfr");/*Swiss721light*/font-style:normal,italic;font-weight:200;}@font-face{font-family:"Swiss721";src:url("swiss721.pfr");/*TheregularSwiss721*/}@font-face{font-family:"Swiss721";src:url("swiss721md.pfr");/*Swiss721medium*/font-style:normal,italic;font-weight:500;}@font-face{font-family:"Swiss721";src:url("swiss721hvy.pfr");/*Swiss721heavy*/font-style:normal,italic;font-weight:700;}@font-face{font-family:"Swiss721";src:url("swiss721blk.pfr");/*Swiss721black*/font-style:normal,italic;font-weight:800,900;/*notetheinterestingproblemthatthe900weightitalicdoesn'texist*/}@font-face{font-family:"Swiss721";src:url(swiss721.pfr);/*ThecondensedSwiss721*/font-stretch:condensed;}@font-face{font-family:"Swiss721";src:url(swiss721.pfr);/*TheexpandedSwiss721*/font-stretch:expanded;}15.4FontCharacteristics15.4.1IntroducingFontCharacteristicsInthissectionarelistedthefontcharacteristicsthathavebeenfoundusefulforclient-sidefontmatching,synthesis,anddownloadforheterogeneousplatformsaccessingtheWeb.ThedatamaybeusefulforanymediumthatneedstousefontsontheWebbysomeothermeansthanphysicalembeddingofthefontdatainsidethemedium.Thesecharacteristicsareusedtocharacterizefonts.TheyarenotspecifictoCSS,ortostylesheets.InCSS,eachcharacteristicisdescribedbyafontdescriptor.ThesecharacteristicscouldalsobemappedontoVRMLnodes,orCGMApplicationStructures,oraJavaAPI,oralternativestylesheetlanguages.Fontsretrievedbyonemediumandstoredinaproxycachecouldbere-usedbyanothermedium,savingdownloadtimeandnetworkbandwidth,ifacommonsystemoffontcharacteristicsareusedthroughout.Anon-exhaustivelistofexamplesofsuchmediaincludes:2-DvectorformatsComputerGraphicsMetafileSimpleVectorFormat3-DgraphicsformatsVRML3DMFObjectembeddingtechnologiesJavaActive-XObliq15.4.2FullfontnameThisisthefullnameofaparticularfaceofafontfamily.Ittypicallyincludesavarietyofnon-standardizedtextualqualifiersoradornmentsappendedtothefontfamilyname.Itmayalsoincludeafoundrynameorabbreviation,oftenprependedtothefontfamilyname.Itisonlyusedtorefertolocallyinstalledfonts,becausetheformatoftheadornednamecanvaryfromplatformtoplatform.Itmustbequoted.Forexample,thefontfamilynameoftheTrueTypefontandthePostScriptnamemaydifferintheuseofspacecharacters,punctuation,andintheabbreviationofsomewords(e.g.,tomeetvarioussystemorprinterinterpreterconstraintsonlengthofnames).Forexample,spacesarenotallowinaPostScriptname,butarecommoninfullfontnames.TheTrueTypenametablecanalsocontainthePostScriptname,whichhasnospaces.Thenameofthefontdefinitionisimportantbecauseitisthelinktoanylocallyinstalledfonts.Itisimportantthatthenameberobust,bothwithrespecttoplatformandapplicationindependence.Forthisreason,thenameshouldbeonethatisnotapplication-orlanguage-specific.Theidealsolutionwouldbetohaveanamethatuniquelyidentifieseachcollectionoffontdata.Thisnamedoesnotexistincurrentpracticeforfontdata.Fontswiththesamefacenamecanvaryoveranumberofdescriptors.Someofthesedescriptors,suchasdifferentcomplementsofglyphsinthefont,maybeinsignificantiftheneededglyphsareinthefont.Otherdescriptors,suchasdifferentwidthmetrics,makefontswiththesamenameincompatible.Itdoesnotseempossibletodefinearulethatwillalwaysidentifyincompatibilities,butwillnotpreventtheuseofaperfectlysuitablelocalcopyofthefontdatawithagivenname.Therefore,onlytherangeofISO10646characterswillbeusedtoqualifymatchesforthefontfacename.Sinceaprimegoalofthefontfacenameinthefontdefinitionistoallowauseragenttodeterminewhenthereisalocalcopyofthespecifiedfontdata,thefontfacenamemustbeanamethatwillbeinalllegitimatecopiesofthefontdata.Otherwise,unnecessaryWebtrafficmaybegeneratedduetomissedmatchesforthelocalcopy.15.4.3CoordinateunitsontheemsquareCertainvalues,suchaswidthmetrics,areexpressedinunitsthatarerelativetoanabstractsquarewhoseheightistheintendeddistancebetweenlinesoftypeinthesametypesize.Thissquareiscalledtheemsquareanditisthedesigngridonwhichtheglyphoutlinesaredefined.ThevalueofthisdescriptorspecifieshowmanyunitstheEMsquareisdividedinto.Commonvaluesareforexample250(Intellifont),1000(Type1)and2048(TrueType,TrueTypeGXandOpenType).Ifthisvalueisnotspecified,itbecomesimpossibletoknowwhatanyfontmetricsmean.Forexample,onefonthaslowercaseglyphsofheight450;anotherhassmalleronesofheight890!Thenumbersareactuallyfractions;thefirstfonthas450/1000andthesecondhas890/2048whichisindeedsmaller.15.4.4CentralBaselineThisgivesthepositionintheemsquareofthecentralbaseline.Thecentralbaselineisusedbyideographicscriptsforalignment,justasthebottombaselineisusedforLatin,Greek,andCyrillicscripts.15.4.5FontEncodingEitherexplicitlyorimplicitly,eachfonthasatableassociatedwithit,thefontencodingtable,thattellswhatcharactereachglyphrepresents.Thistableisalsoreferredtoasanencodingvector.Infact,manyfontscontainseveralglyphsforthesamecharacter.Whichofthoseglyphsshouldbeuseddependseitherontherulesofthelanguage,oronthepreferenceofthedesigner.InArabic,forexample,alllettershavefour(ortwo)differentshapes,dependingonwhethertheletterisusedatthestartofaword,inthemiddle,attheend,orinisolation.Itisthesamecharacterinallcases,andthusthereisonlyonecharacterinthesourcedocument,butwhenprinted,itlooksdifferenteachtime.Therearealsofontsthatleaveittothegraphicdesignertochoosefromamongvariousalternativeshapesprovided.Unfortunately,CSS2doesn'tyetprovidethemeanstoselectthosealternatives.Currently,itisalwaysthedefaultshapethatischosenfromsuchfonts.15.4.6FontfamilynameThisspecifiesthefamilynameportionofthefontfacename.Forexample,thefamilynameforHelvetica-BoldisHelveticaandthefamilynameofITCStoneSerifSemiboldItalicisITCStoneSerif.Somesystemstreatadornmentsrelatingtocondensedorexpandedfacesasiftheywerepartofthefamilyname.15.4.7GlyphwidthsThisisalistofwidths,onthedesigngrid,fortheglyphcorrespondingtoeachcharacter.ThelistisorderedbyISO10646codepoint.Widthscannotusefullybespecifiedwhenmorethanoneglyphmapstothesamecharacterorwhentherearemandatoryligatures.15.4.8HorizontalstemwidthThisvaluereferstothedominantstemofthefont.Theremaybetwoormoredesignedwidths.Forexample,themainverticalstemsofRomancharacterswilldifferfromthethinstemsonserifed"M"and"N",plustheremaybedifferentwidthsforuppercaseandlowercasecharactersinthesamefont.Also,eitherbydesignorbyerror,allstemsmayhaveslightlydifferentwidths.15.4.9HeightofuppercaseglyphsThismeasurementisthey-coordinateofthetopofflatuppercaselettersinLatin,Greek,andCyrillicscripts,measuredfromthebaseline.Thisdescriptorisnotnecessarilyusefulforfontsthatdonotcontainanyglyphsfromthesescripts.15.4.10HeightoflowercaseglyphsThismeasurementisthey-coordinateofthetopofunaccented,non-ascendinglowercaselettersinLatin,GreekandCyrillicscripts,measuredfromthebaseline.Flat-toppedlettersareused,ignoringanyopticalcorrectionzone.Thisisusuallyusedasaratiooflowercasetouppercaseheightsasameanstocomparefontfamilies.Thisdescriptorisnotusefulforfontsthatdonotcontainanyglyphsfromthesescripts.Sincetheheightsoflowercaseanduppercaselettersareoftenexpressedasaratioforcomparingdifferentfonts,itmaybeusefultosetboththelowercaseanduppercaseheightstothesamevalueforunicameralscriptssuchasHebrew,whereformixedLatinandHebrewtext,theHebrewcharactersaretypicallysetataheightmidwaybetweentheuppercaseandlowercaseheightsoftheLatinfont.15.4.11LowerBaselineThisgivesthepositionintheemsquareofthelowerbaseline.ThelowerbaselineisusedbyLatin,Greek,andCyrillicscriptsforalignment,justastheupperbaselineisusedforSanscrit-derivedscripts.15.4.12MathematicalBaselineThisgivesthepositionintheemsquareofthemathematicalbaseline.Themathematicalbaselineisusedbymathematicalsymbolsforalignment,justasthelowerbaselineisusedforLatin,Greek,andCyrillicscripts.15.4.13MaximalboundingboxThemaximalboundingboxisthesmallestrectangleenclosingtheshapethatresultsifallglyphsinthefontareplacedwiththeiroriginscoincident,andthenpainted.Ifadynamicallydownloadablefonthasbeengeneratedbysubsettingaparentfont,thebboxshouldbethatoftheparentfont.15.4.14MaximumunaccentedheightThismeasurement,ontheemsquare,isfromthebaselinetothehighestpointreachedbyanyglyph,excludinganyaccentsordiacriticalmarks.15.4.15MaximumunaccenteddepthThismeasurement,ontheemsquare,isfromthebaselinetothelowestpointreachedbyanyglyph,excludinganyaccentsordiacriticalmarks.15.4.16Panose-1numberPanose-1isanindustrystandardTrueTypefontclassificationandmatchingtechnology.ThePANOSEsystemconsistsofasetoftennumbersthatcategorizethekeyattributesofaLatintypeface,aclassificationprocedureforcreatingthosenumbers,andMappersoftwarethatdeterminestheclosestpossiblefontmatchgivenasetoftypefaces.Thesystemcould,withmodification,alsobeusedforGreekandCyrillic,butisnotsuitableforunicameralandideographicscripts(Hebrew,Armenian,Arabic,Chinese/Japanese/Korean).15.4.17RangeofISO10646charactersThisindicatestheglyphrepertoireofthefont,relativetoISO10646(Unicode).Sincethisissparse(mostfontsdonotcoverthewholeofISO10646)thisdescriptorlistsblocksorrangesthatdohavesomecoverage(nopromiseismadeofcompletecoverage)andisusedtoeliminateunsuitablefonts(onesthatwillnothavetherequiredglyphs).Itdoesnotindicatethatthefontdefinitelyhastherequiredglyphs,onlythatitisworthdownloadingandlookingatthefont.See[ISO10646]forinformationaboutusefuldocuments.ThismethodisextensibletofutureallocationofcharactersinUnicode,withoutchangeofsyntaxandwithoutinvalidatingexistingcontent.Fontformatsthatdonotincludethisinformation,explicitlyorindirectly,maystillusethischaracteristic,butthevaluemustbesuppliedbythedocumentorstylesheetauthor.Thereareotherclassificationsintoscripts,suchastheMonotypesystem(see[MONOTYPE])andaproposedISOscriptsystem.Thesearenotreadilyextensible.Becauseofthis,classificationofglyphrepertoiresbytherangeofISO10646charactersthatmayberepresentedwithaparticularfontisusedinthisspecification.Thissystemisextensibletocoveranyfutureallocation.15.4.18TopBaselineThisgivesthepositionintheemsquareofthetopbaseline.ThetopbaselineisusedbySanscrit-derivedscriptsforalignment,justasthebottombaselineisusedforLatin,Greek,andCyrillicscripts.15.4.19VerticalstemwidthThisisthewidthofvertical(ornear-vertical)stemsofglyphs.Thisinformationisoftentiedtohinting,andmaynotbedirectlyaccessibleinsomefontformats.Themeasurementshouldbeforthedominantverticalsteminthefontbecausetheremightbedifferentgroupingsofverticalstems(e.g.,onemainone,andonelighterweightoneasforanuppercaseMorN).15.4.20VerticalstrokeangleThisistheangle,indegreescounterclockwisefromthevertical,ofthedominantverticalstrokesofthefont.Thevalueisnegativeforfontsthatslopetotheright,asalmostallitalicfontsdo.Thisdescriptormayalsobespecifiedforobliquefonts,slantedfonts,scriptfonts,andingeneralforanyfontwhoseverticalstrokesarenotpreciselyvertical.Anon-zerovaluedoesnotofitselfindicateanitalicfont.15.5FontmatchingalgorithmThisspecificationextendsthealgorithmgivenintheCSS1specification.ThisalgorithmreducesdowntothealgorithmintheCSS1specificationwhentheauthorandreaderstylesheetsdonotcontainany@font-facerules.Matchingofdescriptorstofontfacesmustbedonecarefully.Thedescriptorsarematchedinawell-definedordertoinsurethattheresultsofthismatchingprocessareasconsistentaspossibleacrossUAs(assumingthatthesamelibraryoffontfacesandfontdescriptionsispresentedtoeachofthem).Thisalgorithmmaybeoptimized,providedthatanimplementationbehavesasifthealgorithmhadbeenfollowedexactly.Theuseragentmakes(oraccesses)adatabaseofrelevantfont-facedescriptorsofallthefontsofwhichtheUAisaware.Iftherearetwofontswithexactlythesamedescriptors,oneofthemisignored.TheUAmaybeawareofafontbecause:ithasbeeninstalledlocallyitisdeclaredusingan@font-faceruleinoneofthestylesheetslinkedtoorcontainedinthecurrentdocumentitisusedintheUAdefaultstylesheet,whichconceptuallyexistsinallUAsandisconsideredtohavefull@font-facerulesforallfontswhichtheUAwillusefordefaultpresentation,plus@font-facerulesforthefivespecialgenericfontfamilies(see'font-family')definedinCSS2Atagivenelementandforeachcharacterinthatelement,theUAassemblesthefontpropertiesapplicabletothatelement.Usingthecompletesetofproperties,theUAusesthe'font-family'descriptortochooseatentativefontfamily.Thus,matchingonafamilynamewillsucceedbeforematchingonsomeotherdescriptor.Theremainingpropertiesaretestedagainstthefamilyaccordingtothematchingcriteriadescribedwitheachdescriptor.Iftherearematchesforalltheremainingproperties,thenthatisthematchingfontfaceforthegivenelement.Ifthereisnomatchingfontfacewithinthe'font-family'beingprocessedbystep2,UAsthatimplementintelligentmatchingmayproceedtoexamineotherdescriptorssuchasx-height,glyphwidths,andpanose-1toidentifyadifferenttentativefontfamily.Iftherearematchesforalltheremainingdescriptors,thenthatisthematchingfontfaceforthegivenelement.The'font-family'descriptorthatisreflectedintotheCSS2propertiesisthefontfamilythatwasrequested,notwhatevernametheintelligentlymatchedfontmayhave.UAsthatdonotimplementintelligentmatchingareconsideredtofailatthisstep.Ifthereisnomatchingfontfacewithinthe'font-family'beingprocessedbystep3,UAsthatimplementfontdownloadingmayproceedtoexaminethe'src'descriptorofthetentativefontfaceidentifiedinstep2or3toidentifyanetworkresourcethatisavailable,andofthecorrectformat.Iftherearematchesforalltheremainingdescriptors,thenthatisthematchingfontfaceforthegivenelementandtheUAmayattempttodownloadthisfontresource.TheUAmaychoosetoblockonthisdownloadormaychoosetoproceedtothenextstepwhilethefontdownloads.UAsthatdonotimplementfontdownload,orarenotconnectedtoanetwork,orwheretheuserpreferenceshavedisabledfontdownload,orwheretherequestedresourceisunavailableforwhateverreason,orwherethedownloadedfontcannotbeusedforwhateverreason,areconsideredtofailatthisstep.Ifthereisnomatchingfontfacewithinthe'font-family'beingprocessedbystep3,UAsthatimplementfontsynthesismayproceedtoexamineotherdescriptorssuchas'x-height',glyphwidths,and'panose-1'toidentifyadifferenttentativefontfamilyforsynthesis.Iftherearematchesforalltheremainingdescriptors,thenthatisthematchingfontfaceforthegivenelementandsynthesisofthefauxfontmaybegin.UAsthatdonotimplementfontsynthesisareconsideredtofailatthisstep.Ifallofsteps3,4and5fail,andifthereisanextalternative'font-family'inthefontset,thenrepeatfromstep2withthenextalternative'font-family'.Ifthereisamatchingfontface,butitdoesn'tcontainglyph(s)forthecurrentcharacter(s),andifthereisanextalternative'font-family'inthefontsets,thenrepeatfromstep2withthenextalternative'font-family'.The'unicode-range'descriptormaybeusedtorapidlyeliminatefromconsiderationthosefontfacesthatdonothavethecorrectglyphs.Ifthe'unicode-range'descriptorindicatesthatafontcontainssomeglyphsinthecorrectrange,itmaybeexaminedbytheUAtoseeifithasthatparticularone.Ifthereisnofontwithinthefamilyselectedin2,thenusetheinheritedorUA-dependent'font-family'valueandrepeatfromstep2,usingthebestmatchthatcanbeobtainedwithinthisfont.Ifaparticularcharactercannotbedisplayedusingthisfont,theUAshouldindicatethatacharacterisnotbeingdisplayed(forexample,usingthe'missingcharacter'glyph).UAsthatimplementprogressiverenderingandhavependingfontdownloadsmay,oncedownloadissuccessful,usethedownloadedfontasafontfamily.Ifthedownloadedfontismissingsomeglyphsthatthetemporaryprogressivefontdidcontain,thedownloadedfontisnotusedforthatcharacterandthetemporaryfontcontinuestobeused.Note.TheabovealgorithmcanbeoptimizedtoavoidhavingtorevisittheCSS2propertiesforeachcharacter.Theper-descriptormatchingrulesfrom(2)aboveareasfollows:'font-style'istriedfirst.'italic'willbesatisfiedifthereiseitherafaceintheUA'sfontdatabaselabeledwiththeCSSkeyword'italic'(preferred)or'oblique'.Otherwisethevaluesmustbematchedexactlyorfont-stylewillfail.'font-variant'istriednext.'normal'matchesafontnotlabeledas'small-caps';'small-caps'matches(1)afontlabeledas'small-caps',(2)afontinwhichthesmallcapsaresynthesized,or(3)afontwherealllowercaselettersarereplacedbyuppercaseletters.Asmall-capsfontmaybesynthesizedbyelectronicallyscalinguppercaselettersfromanormalfont.'font-weight'ismatchednext,itwillneverfail.(See'font-weight'below.)'font-size'mustbematchedwithinaUA-dependentmarginoftolerance.(Typically,sizesforscalablefontsareroundedtothenearestwholepixel,whilethetoleranceforbitmappedfontscouldbeaslargeas20%.)Furthercomputations,e.g.,by'em'valuesinotherproperties,arebasedonthe'font-size'valuethatisused,nottheonethatisspecified.15.5.1MappingfontweightvaluestofontnamesThe'font-weight'propertyvaluesaregivenonanumericalscaleinwhichthevalue'400'(or'normal')correspondstothe"normal"textfaceforthatfamily.TheweightnameassociatedwiththatfacewilltypicallybeBook,Regular,Roman,NormalorsometimesMedium.Theassociationofotherweightswithinafamilytothenumericalweightvaluesisintendedonlytopreservetheorderingofweightswithinthatfamily.Useragentsmustmapnamestovaluesinawaythatpreservesvisualorder;afacemappedtoavaluemustnotbelighterthanfacesmappedtolowervalues.Thereisnoguaranteeonhowauseragentwillmapfontfaceswithinafamilytoweightvalues.However,thefollowingheuristicstellhowtheassignmentisdoneintypicalcases:Ifthefontfamilyalreadyusesanumericalscalewithninevalues(ase.g.,OpenTypedoes),thefontweightsshouldbemappeddirectly.IfthereisbothafacelabeledMediumandonelabeledBook,Regular,RomanorNormal,thentheMediumisnormallyassignedtothe'500'.Thefontlabeled"Bold"willoftencorrespondtotheweightvalue'700'.Iftherearefewerthen9weights120%/120% fantasy }
In the family, the default algorithm for fillingsecond rule, the "holes" is as follows. If '500' is unassigned, it will be assignedfont size percentage value ('80%') refers
to the samefont as '400'. If anysize of the values '600', '700', '800', or '900' remains unassigned, they are assigned to the same face asparent element. In the next darker assigned keyword, if any, orthird rule, the next lighter one otherwise. If any of '300', '200', or '100' remains unassigned, it is assignedline
height percentage refers to the next lighter assigned keyword, if any, or the next darker otherwise. There is no guarantee that there will be a darker face for eachfont size of the 'font-weight' values; for example, some fonts may have only a normal and a bold face, others may have eight different face weights. The following two examples show typical mappings. Assume four weightselement itself.
In the "Rattlesnake" family, from lightest to darkest: Regular, Medium, Bold, Heavy.first example of font-weight mapping Available faces Assignments Filling the holes "Rattlesnake Regular" 400 100, 200, 300 "Rattlesnake Medium" 500 "Rattlesnake Bold" 700 600 "Rattlesnake Heavy" 800 900 Assume six weights in the "Ice Prawn" family: Book, Medium, Bold, Heavy, Black, ExtraBlack. Note that in this instancethree rules above, the user agent has decided'font-style', 'font-variant'
and 'font-weight' are not explicitly mentioned, which means they are
all three set to assign a numerictheir initial value ('normal'). The fourth rule sets
the 'font-weight' to "Example2 ExtraBlack". Second example of font-weight mapping Available faces Assignments Filling'bold', the 'font-style' to 'italic' and
implicitly sets 'font-variant' to 'normal'.
The fifth rule sets the 'font-variant' ('small-caps'), the
holes "Ice Prawn Book" 400 100, 200, 300 "Ice Prawn Medium" 500 "Ice Prawn Bold" 700 600 "Ice Prawn Heavy" 800 "Ice Prawn Black" 900 "Ice Prawn ExtraBlack" (none) 15.5.2 Examples'font-size' (120% of the parent's font), the 'line-height' (120% times
the font matching Example(s):size) and the 'font-family' ('fantasy'). It follows that the
keyword 'normal' applies to the two remaining properties: 'font-style'
and 'font-weight'.
The following example defines a specific font face, Alabama Italic. A panosevalues refer to system fonts:
System fonts may only be set as a whole; that is, the adornedfont
name is Alabama Italic. @font-face { src: local("Alabama Italic"), url(http://www.fonts.org/A/alabama-italic) format("truetype"); panose-1: 2 4 5 2 5 4 5 9 3 3; font-family: Alabama, serif; font-weight: 300, 400, 500; font-style: italic, oblique; } Example(s):family, size, weight, style, etc. are all set at the next example definessame time.
These values may then be altered individually if desired. If no
font with the indicated characteristics exists on a family of fonts.given platform,
the user agent should either intelligently substitute (e.g., a single URI is provided for retrievingsmaller
version of the 'caption' font data. This data file will contain multiple styles and weights ofmight be used for the named'small-caption'
font), or substitute a user agent default font. Once oneAs for regular fonts,
if, for a system font, any of the individual properties are not part
of these @font-face definitions has been dereferenced,the data willoperating system's available user preferences, those properties
should be in the UA cache for other facesset to their initial values.
That use the same URI. @font-face { src: local("Helvetica Medium"), url(http://www.fonts.org/sans/Helvetica_family) format("truedoc"); font-family: "Helvetica"; font-style: normal } @font-face { src: local("Helvetica Oblique"), url("http://www.fonts.org/sans/Helvetica_family") format("truedoc"); font-family: "Helvetica"; font-style: oblique; slope: -18 } Example(s): The following example groups three physicalis why this property is "almost" a shorthand property: system
fonts into one virtual fontcan only be specified with extended coverage. In each case,this property, not with 'font-family' itself, so 'font' allows authors to do more than the
adorned font name issum of its subproperties. However, the individual properties such as 'font-weight' are still given invalues taken from the src descriptor to allow locally installed versions tosystem font, which can be preferentially used if available. A fourth rule points to a font with the same coverage, but contained in a single resource. @font-face { font-family: Excelsior; src: local("Excelsior Roman"), url("http://site/er") format("intellifont"); unicode-range: U+??; /* Latin-1 */ } @font-faceindependently varied.
button { font-family: Excelsior; src: local("Excelsior EastA Roman"), url("http://site/ear") format("intellifont"); unicode-range: U+100-220; /* Latin Extended A and B */font: 300 italic 1.3em/1.7em "FB Armada", sans-serif }
@font-facebutton p { font-family: Excelsior; src: local("Excelsior Cyrillic Upright"), url("http://site/ecr") format("intellifont"); unicode-range: U+4??; /* Cyrillic */font: menu }
@font-facebutton p em { font-family: Excelsior; src: url("http://site/excels") format("truedoc"); unicode-range: U+??,U+100-220,U+4??;font-weight: bolder }
Example(s): This next example might be found in a UA's default style sheet. It implementsIf the CSS2 genericfont family, serif by mapping itused for dropdown menus on a particular system
happened to be, for example, 9-point Charcoal, with a wide varietyweight of serif fonts600, then P
elements that might exist on various platforms. No metrics arewere descendants of BUTTON would be displayed as if
this rule were in effect:
button p { font: 600 9px Charcoal }
Because the 'font' shorthand
property resets any property not explicitly given since these vary amonga value
to its initial value, this has the possible alternatives. @font-facesame effect as this declaration:
button p {
src: local("Palatino"), local("Times New Roman"), local("New York"), local("Utopia"), url("http://somewhere/free/font");font-family: serif; font-weight: 100, 200, 300, 400, 500;Charcoal;
font-style: normal;
font-variant: normal;
font-weight: 600;
font-size: all9px;
line-height: normal;
}