Internet Engineering Task Force (IETF) C. Lilley
Request for Comments: 8081 W3C
Category: Standards Track February 2017
ISSN: 2070-1721
The "font" Top-Level Media Type
Abstract
This memo serves to register and document the "font" top-level media
type, under which subtypes for representation formats for fonts may
be registered. This document also serves as a registration
application for a set of intended subtypes, which are representative
of some existing subtypes already in use, and currently registered
under the "application" tree by their separate registrations.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8081.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Lilley Standards Track [Page 1]
RFC 8081 The 'font' Top-Level Type February 2017
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background and Justification . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. Definition and Encoding . . . . . . . . . . . . . . . . . 5
4.2. Fragment Identifiers for Font Collections . . . . . . . . 5
4.3. Registration Procedure . . . . . . . . . . . . . . . . . 6
4.4. Subtype Registrations . . . . . . . . . . . . . . . . . . 6
4.4.1. Generic SFNT Font Type . . . . . . . . . . . . . . . 6
4.4.2. TTF Font Type . . . . . . . . . . . . . . . . . . . . 9
4.4.3. OpenType Layout (OTF) Font Type . . . . . . . . . . . 10
4.4.4. Collection Font Type . . . . . . . . . . . . . . . . 12
4.4.5. WOFF 1.0 . . . . . . . . . . . . . . . . . . . . . . 14
4.4.6. WOFF 2.0 . . . . . . . . . . . . . . . . . . . . . . 15
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Normative References . . . . . . . . . . . . . . . . . . 16
5.2. Informative References . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
The process of setting type in computer systems and other forms of
text presentation systems uses fonts in order to provide visual
representations of the glyphs. Just as with images, for example,
there are a number of ways to represent the visual information of the
glyphs. Early font formats often used bitmaps, as these could have
been carefully tuned for maximum readability at a given size on low-
resolution displays. More recently, scalable vector outline fonts
have come into widespread use. In these fonts, the outlines of the
glyphs are described, and the presentation system renders the outline
in the desired position and size.
Over time, a number of standard formats for recording font
descriptions have evolved. Internet Media Types [RFC6838] are used
to label content carried over Internet protocols. This document
defines a new top-level type "font" according to Section 4.2.7 of
[RFC6838]. This top-level type indicates that the content specifies
font data. Under this top-level type, different representation
formats of fonts may be registered.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Lilley Standards Track [Page 2]
RFC 8081 The 'font' Top-Level Type February 2017
2. Background and Justification
Historically, there has not been a registration of formats for fonts.
More recently, there have been several representation formats
registered as media subtypes under the "application" top-level type
(for example, "application/font-woff"). However, with the rapid
adoption of web fonts (based on the data from HTTP Archive
[HTTP-Archive-Trends] showing a huge increase in web font usage from
1% in the end of 2010 to 50% across all sites in the beginning of
2015), custom fonts on the web have become a core web resource. As
the in-depth analysis [Font-Media-Type-Analysis] shows, the lack of
the intuitive top-level font type is causing significant confusion
among developers -- while currently defined font subtypes are
severely under-utilized, there are many more sites that already use
nonexistent (but highly intuitive) media types such as "font/woff",
"font/ttf", and "font/truetype". At the same time, the majority of
sites resort to using generic types such as "application/octet-
stream", "text/plain", and "text/html", or use unregisterable types
such as "application/x-font-ttf".
Contrary to the expectations of the W3C WebFonts WG, which developed
Web Open Font Format (WOFF), the officially defined media types such
as "application/font-woff" and "application/font-sfnt" see a very
limited use -- their adoption rates trail far behind as the actual
use of web fonts continues to increase. The members of the W3C
WebFonts WG concluded that the use of the "application" top-level
type is not ideal. First, the "application" sub-tree is treated
(correctly) with great caution with respect to viruses and other
active code. Secondly, the lack of a top-level type means that there
is no opportunity to have a common set of optional parameters, such
as are specified here. Third, fonts have a unique set of licensing
and usage restrictions, which makes it worthwhile to identify this
general category with a unique top-level type.
The W3C WebFonts WG decided [WG-tlt] that the situation can be
significantly improved if a set of font media types is registered
using "font" as a dedicated top-level type. Based on the data
analysis presented above, we conclude that it is the presence of
simple and highly intuitive media types for images that caused their
widespread adoption, where the correct usage of existing media types
reaches over 97% for all subtypes in the "image" tree. The WG
considers that, keeping in mind a rapid adoption of fonts on the web,
the registration of the top-level media type for fonts along with the
intuitive set of subtypes that reflect popular and widely used data
formats would further stimulate the adoption of web fonts,
significantly simplify web server configuration process, and
facilitate the proper use of media types for fonts.
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RFC 8081 The 'font' Top-Level Type February 2017
3. Security Considerations
Fonts are interpreted data structures that represent collections of
different tables containing data that represent different types of
information, including glyph outlines in various formats, hinting
instructions, metrics and layout information for multiple languages
and writing systems, rules for glyph substitution and positioning,
etc. In particular, the hinting instructions for TrueType glyphs
represent executable code that has the potential to be maliciously
constructed (for example, intended to hang the interpreter). There
are many existing, already standardized font table tags and formats
that allow an unspecified number of entries containing predefined
data fields for storage of variable-length binary data. Many
existing font formats (TrueType [truetype-wiki], OpenType and OFF
[opentype-wiki], SIL Graphite, WOFF, etc.) are based on the table-
based SFNT (scalable font) format, which is extremely flexible,
highly extensible, and offers an opportunity to introduce additional
table structures when needed, in an upward-compatible way that would
not affect existing font rendering engines and text layout
implementations. However, this very extensibility may present
specific security concerns -- the flexibility and ease of adding new
data structures makes it easy for any arbitrary data to be hidden
inside a font file. There is a significant risk that the flexibility
of font data structures may be exploited to hide malicious binary
content disguised as a font data component.
Fonts may contain 'hints', which are programmatic instructions that
are executed by the font engine for the alignment of graphical
elements of glyph outlines with the target display pixel grid.
Depending on the font technology utilized in the creation of a font,
these hints may represent active code interpreted and executed by the
font rasterizer. Even though hints operate within the confines of
the glyph outline conversion system and have no access outside the
font rendering engine, hint instructions can be quite complex, and a
maliciously designed complex font could cause undue resource
consumption (e.g., memory or CPU cycles) on a machine interpreting
it. Indeed, fonts are sufficiently complex that most (if not all)
interpreters cannot be completely protected from malicious fonts
without undue performance penalties.
Widespread use of fonts as necessary components of visual content
presentation warrants that careful attention should be given to
security considerations whenever a font is either embedded into an
electronic document or transmitted alongside media content as a
linked resource. While many existing font formats provide certain
levels of protection of data integrity (such mechanisms include,
e.g., checksums and digital signatures), font data formats provide
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RFC 8081 The 'font' Top-Level Type February 2017
neither privacy nor confidentiality protection internally; if needed,
such protection should be provided externally.
4. IANA Considerations
This specification registers a new top-level type, "font", in the
standards tree, adds it as an alternative value of "Type Name" in the
media types registration form [Media-Type-Registration], and
registers several subtypes for it.
4.1. Definition and Encoding
The "font" as the primary media content type indicates that the
content identified by it requires a certain graphic subsystem such as
a font rendering engine (and, in some cases, a text layout and a
shaping engine) to process it as font data, which in turn may require
a certain level of hardware capabilities such as certain levels of
CPU performance and available memory. The "font" media type does not
provide any specific information about the underlying data format and
how the font information should be interpreted -- the subtypes
defined within a "font" tree name the specific font formats.
Unrecognized subtypes of "font" should be treated as "application/
octet-stream". Implementations may pass unrecognized subtypes to a
common font-handling system, if such a system is available.
4.2. Fragment Identifiers for Font Collections
Fragment identifiers for font collections identify one font in the
collection by the PostScript name (name ID=6) [ISO.14496-22.2015].
This is a string, no longer than 63 characters and restricted to the
printable ASCII subset, codes 33 ? 126, except for the 10 characters
'[', ']', '(', ')', '{', '}', '<', '>', '/', '%', which are forbidden
by [ISO.14496-22.2015].
In addition, the following 6 characters could occur in the PostScript
name but are forbidden in fragments by [RFC3986], and thus must be
escaped: '"', '#', '\', '^', '`', '|'.
If (following un-escaping) this string matches one of the PostScript
names in the name table, that font is selected. For example, "#Foo-
Bold" refers to the font with PostScript name "Foo-Bold" and
"#Caret%5Estick" refers to the font with PostScript name
"Caret^stick". If the name does not match, or if a fragment is not
specified, the first font in the collection is matched. Note that
the order of fonts in collections may change as the font is revised,
so relying on a particular font in a collection always being first is
unwise.
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4.3. Registration Procedure
New font formats should be registered using the online form
[Media-Type-Registration]. [RFC6838] should be consulted on
registration procedures. In particular, the font specification
should preferably be freely available. If the font format can
contain multiple fonts, a fragment identifier syntax should also be
defined.
Note that new parameter sub-values may be defined in the future. If
an implementation does not recognize a sub-value in the comma-
separated list, it should ignore the sub-value and continue
processing the other sub-values in the list.
4.4. Subtype Registrations
In this section, the initial entries under the top-level 'font' media
type are specified. They also serve as examples for future
registrations.
For each subtype, an @font-face format identifier is listed. This is
for use with the @font-face src descriptor, defined by the Cascading
Style Sheets Level 3 (CSS3) Fonts specification
[W3C.CR-css-fonts-3-20131003]. That specification is normative; the
identifiers here are informative.
4.4.1. Generic SFNT Font Type
Type name: font
Subtype name: sfnt
Required parameters: None
Optional parameters:
1) Name: outlines
Values: a comma-separated subset of True Type Font (TTF),
Compact Font Format (CFF), and SVG
This parameter can be used to specify the type of outlines
provided by the font. The value "TTF" shall be used when a
font resource contains glyph outlines in TrueType format, the
value "CFF" shall be used to identify fonts containing
PostScript/CFF outlines [cff-wiki], and the value SVG
[svg-wiki] shall be used to identify fonts that include SVG
outlines. TTF, CFF, or SVG outlines can be present in various
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combinations in the same font file; therefore, this optional
parameter is a list containing one or more items, separated by
commas. Order in the list is not significant.
2) Name: layout
Values: a comma-separated subset of OTL, Apple Advanced
Typography (AAT), and SIL
This parameter identifies the type of implemented support for
advanced text layout features. The predefined values "OTL",
"AAT", and "SIL", respectively, indicate support for OpenType
text layout, Apple Advanced Typography, or Graphite SIL. More
than one shaping and layout mechanism may be provided by the
same font file; therefore, this optional parameter is a list
containing one or more items, separated by commas. Order in
the list is not significant.
Encoding considerations: Binary
Interoperability considerations: As it was noted in the first
paragraph of the Security Considerations section, a single font
file can contain encoding of the same glyphs using several
different representations, e.g., both TrueType and PostScript
(CFF) outlines. Existing font rendering engines may not be able
to process some of the particular outline formats, and downloading
a font resource that contains only an unsupported glyph data
format would be futile. Therefore, it is useful to clearly
identify the format of the glyph outline data within a font using
an optional parameter, and allow applications to make decisions
about downloading a particular font resource sooner. Similarly,
another optional parameter identifies the type of text shaping and
layout mechanism that is provided by a font.
Published specification: ISO/IEC 14496-22 "Open Font Format" (OFF)
specification [ISO.14496-22.2015] being developed by ISO/IEC SC29/
WG11.
Applications that use this media type: All applications that are
able to create, edit, or display textual media content.
Note that "font/sfnt" is an abstract type from which the (widely
used in practice) "font/ttf" and "font/otf" types are conceptually
derived. Use of "font/sfnt" is likely to be rare in practice, and
might be confined to:
Uncommon combinations such as "font/sfnt; layout=sil" that do
not have a shorter type
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Cases where a new parameter value is registered
Test cases, experimentation, etc.
Additional information:
Magic number(s): The TrueType fonts and OFF / OpenType fonts
containing TrueType outlines should use 0x00010000 as the
'sfnt' version number.
The OFF / OpenType fonts containing CFF data should use the tag
'OTTO' as the 'sfnt' version number.
File extension(s): Font file extensions used for OFF / OpenType
fonts: .ttf and .otf
Typically, the .ttf extension is only used for fonts containing
TrueType outlines, whereas the .otf extension can be used for
any OpenType/OFF font, and either can be used with the TrueType
or CFF outlines.
Macintosh file type code(s): (no code specified)
Macintosh Universal Type Identifier code: "public.font"
@font-face Format: None
Fragment Identifiers: None
Deprecated Alias: The existing registration "application/font-
sfnt" is deprecated in favor of "font/sfnt".
Person & email address to contact for further information:
Vladimir Levantovsky (vladimir.levantovsky@monotype.com).
Intended usage: COMMON
Restrictions on usage: None
Author: The ISO/IEC 14496-22 "Open Font Format" specification is a
product of the ISO/IEC JTC1 SC29/WG11.
Change controller: The ISO/IEC has change control over this
specification.
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RFC 8081 The 'font' Top-Level Type February 2017
4.4.2. TTF Font Type
Type name: font
Subtype name: ttf
Required parameters: None
Optional parameters:
Name: layout
Values: a comma-separated subset of OTL, AAT, and SIL
This parameter identifies the type of support mechanism for
advanced text layout features. The predefined values "OTL",
"AAT", and "SIL" respectively indicate support for OpenType
text layout, Apple Advanced Typography, or Graphite SIL. More
than one shaping and layout mechanism may be provided by the
same font file; therefore, this optional parameter is a list
containing one or more items, separated by commas. Order in
the list is not significant.
Encoding considerations: Binary
Interoperability considerations: As it was noted in the first
paragraph of Section 3, a single font file can contain encoding of
the same glyphs using several different representations, e.g.,
both TrueType and PostScript (CFF) outlines. Existing font
rendering engines may not be able to process some of the
particular outline formats, and downloading a font resource that
contains only an unsupported glyph data format would be futile.
Therefore, it is useful to clearly identify the format of the
glyph outline data within a font using an optional parameter, and
allow applications to make decisions about downloading a
particular font resource sooner. Similarly, another optional
parameter identifies the type of text shaping and layout mechanism
that is provided by a font.
Published specification: ISO/IEC 14496-22 "Open Font Format" (OFF)
specification [ISO.14496-22.2015] being developed by ISO/IEC SC29/
WG11.
Applications that use this media type: All applications that are
able to create, edit, or display textual media content.
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RFC 8081 The 'font' Top-Level Type February 2017
Additional information:
Magic number(s): The TrueType fonts and OFF / OpenType fonts
containing TrueType outlines should use 0x00010000 as the
'sfnt' version number.
File extension(s): Font file extensions used for TrueType / OFF /
OpenType fonts: .ttf and .otf
Typically, the .ttf extension is only used for fonts containing
TrueType outlines, while the .otf extension may be used for any
OpenType/OFF font, either with TrueType or CFF outlines.
Macintosh file type code(s): (no code specified)
Macintosh Universal Type Identifier code: "public.truetype-font"
@font-face Format: truetype
Fragment Identifiers: None
Person & email address to contact for further information:
Vladimir Levantovsky (vladimir.levantovsky@monotype.com).
Intended usage: COMMON
Restrictions on usage: None
Author: The ISO/IEC 14496-22 "Open Font Format" specification is a
product of the ISO/IEC JTC1 SC29/WG11.
Change controller: The ISO/IEC has change control over this
specification.
4.4.3. OpenType Layout (OTF) Font Type
Type name: font
Subtype name: otf
Required parameters: None
Optional parameters
Name: outlines
Lilley Standards Track [Page 10]
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Values: a comma-separated subset of TTF, CFF, and SVG
This parameter can be used to specify the type of outlines
provided by the font. The value "TTF" shall be used when a
font resource contains glyph outlines in TrueType format, the
value "CFF" shall be used to identify fonts containing
PostScript/CFF outlines, and the value SVG shall be used to
identify fonts that include SVG outlines. TTF, CFF, or SVG
outlines can be present in various combinations in the same
font file; therefore, this optional parameter is a list
containing one or more items, separated by commas. Order in
the list is not significant.
Encoding considerations: Binary
Interoperability considerations: As it was noted in the first
paragraph of the Security Considerations section, a single font
file can contain encoding of the same glyphs using several
different representations, e.g., both TrueType and PostScript
(CFF) outlines. Existing font rendering engines may not be able
to process some of the particular outline formats, and downloading
a font resource that contains only unsupported glyph data format
would be futile. Therefore, it is useful to clearly identify the
format of the glyph outline data within a font using an optional
parameter, and allow applications to make decisions about
downloading a particular font resource sooner. Similarly, another
optional parameter identifies the type of text shaping and layout
mechanism that is provided by a font.
Published specification: ISO/IEC 14496-22 "Open Font Format" (OFF)
specification [ISO.14496-22.2015] being developed by ISO/IEC SC29/
WG11.
Applications that use this media type: All applications that are
able to create, edit, or display textual media content.
Additional information:
Magic number(s): The TrueType fonts and OFF / OpenType fonts
containing TrueType outlines should use 0x00010000 as the
'sfnt' version number.
The OFF / OpenType fonts containing CFF outlines should use the
tag 'OTTO' as the 'sfnt' version number. There is no magic
number for SVG outlines; these are always accompanied by either
TrueType or CFF outlines, and thus use the corresponding magic
number.
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RFC 8081 The 'font' Top-Level Type February 2017
File extension(s): Font file extensions used for OFF / OpenType
fonts: .ttf and .otf
Typically, the .ttf extension is only used for fonts containing
TrueType outlines, while the .otf extension can be used for any
OpenType/OFF font, either with TrueType, CFF, or SVG outlines.
Macintosh file type code(s): (no code specified)
Macintosh Universal Type Identifier code: "public.opentype-font"
@font-face Format: opentype
Fragment Identifiers: None
Person & email address to contact for further information:
Vladimir Levantovsky (vladimir.levantovsky@monotype.com).
Intended usage: COMMON
Restrictions on usage: None
Author: The ISO/IEC 14496-22 "Open Font Format" specification is a
product of the ISO/IEC JTC1 SC29/WG11.
Change controller: The ISO/IEC has change control over this
specification.
4.4.4. Collection Font Type
Type name: font
Subtype name: collection
Required parameters: None
Optional parameters
Name: outlines
Values: a comma-separated subset of TTF, CFF, and SVG
This parameter can be used to specify the type of outlines
provided by the font. The value "TTF" shall be used when a
font resource contains glyph outlines in TrueType format, the
value "CFF" shall be used to identify fonts containing
PostScript/CFF outlines, and the value SVG shall be used to
identify fonts that include SVG outlines. TTF, CFF, or SVG
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RFC 8081 The 'font' Top-Level Type February 2017
outlines can be present in various combinations in the same
font file; therefore, this optional parameter is a list
containing one or more items, separated by commas. Order in
the list is not significant.
Encoding considerations: Binary
Interoperability considerations: As it was noted in the first
paragraph of the Security Considerations section, a single font
file can contain encoding of the same glyphs using several
different representations, e.g., both TrueType and PostScript
(CFF) outlines. Existing font rendering engines may not be able
to process some of the particular outline formats, and downloading
a font resource that contains only unsupported glyph data format
would be futile. Therefore, it is useful to clearly identify the
format of the glyph outline data within a font using an optional
parameter, and allow applications to make decisions about
downloading a particular font resource sooner. Similarly, another
optional parameter identifies the type of text shaping and layout
mechanism that is provided by a font.
Published specification: ISO/IEC 14496-22 "Open Font Format" (OFF)
specification [ISO.14496-22.2015] being developed by ISO/IEC SC29/
WG11.
Applications that use this media type: All applications that are
able to create, edit, or display textual media content.
Additional information:
Magic number(s): The TrueType fonts and OFF / OpenType fonts
containing TrueType outlines should use 0x00010000 as the
'sfnt' version number.
The OFF / OpenType fonts containing CFF outlines should use the
tag 'OTTO' as the 'sfnt' version number. There is no magic
number for SVG outlines; these are always accompanied by either
TrueType or CFF outlines, and thus use the corresponding magic
number.
File extension(s): Font file extensions used for OFF / TrueType
and OpenType fonts: .ttc
Macintosh file type code(s): (no code specified)
Macintosh Universal Type Identifier code: "public.truetype-
collection-font"
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RFC 8081 The 'font' Top-Level Type February 2017
@font-face Format: collection
Fragment Identifiers: See Section 4.2.
Person & email address to contact for further information:
Vladimir Levantovsky (vladimir.levantovsky@monotype.com).
Intended usage: COMMON
Restrictions on usage: None
Author: The ISO/IEC 14496-22 "Open Font Format" specification is a
product of the ISO/IEC JTC1 SC29/WG11.
Change controller: The ISO/IEC has change control over this
specification.
4.4.5. WOFF 1.0
Type name: font
Subtype name: woff
Required parameters: None
Optional parameters: None
Encoding considerations: Binary
Interoperability considerations: None
Published specification: This media type registration updates the
WOFF specification [W3C.REC-WOFF-20121213] at W3C.
Applications that use this media type: WOFF is used by web browsers,
often in conjunction with HTML and CSS.
Additional information:
Magic number(s): The signature field in the WOFF header MUST
contain the "magic number" 0x774F4646 ('wOFF')
File extension(s): woff
Macintosh file type code(s): (no code specified)
Macintosh Universal Type Identifier code: "org.w3.woff"
Lilley Standards Track [Page 14]
RFC 8081 The 'font' Top-Level Type February 2017
@font-face Format: woff
Fragment Identifiers: None
Deprecated Alias: The existing registration "application/font-
woff" is deprecated in favor of "font/woff".
Person & email address to contact for further information:
Chris Lilley (www-font@w3.org).
Intended usage: COMMON
Restrictions on usage: None
Author: The WOFF specification is a work product of the World Wide
Web Consortium's WebFonts working group.
Change controller: The W3C has change control over this
specification.
4.4.6. WOFF 2.0
Type name: font
Subtype name: woff2
Required parameters: None
Optional parameters: None
Encoding considerations: Binary
Interoperability considerations: WOFF 2.0 is an improvement on WOFF
1.0. The two formats have different Internet Media Types and
different @font-face formats, and they may be used in parallel.
Published specification: This media type registration is extracted
from the WOFF 2.0 specification [W3C.CR-WOFF2-20150414] at W3C.
Applications that use this media type: WOFF 2.0 is used by web
browsers, often in conjunction with HTML and CSS.
Additional information:
Magic number(s): The signature field in the WOFF header MUST
contain the "magic number" 0x774F4632 ('wOF2')
File extension(s): woff2
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Macintosh file type code(s): (no code specified)
Macintosh Universal Type Identifier code: "org.w3.woff2"
@font-face Format: woff2
Fragment Identifiers: See Section 4.2.
Person & email address to contact for further information:
Chris Lilley (www-font@w3.org).
Intended usage: COMMON
Restrictions on usage: None
Author: The WOFF2 specification is a work product of the World Wide
Web Consortium's WebFonts working group.
Change controller: The W3C has change control over this
specification.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[W3C.CR-css-fonts-3-20131003]
Daggett, J., "CSS Fonts Module Level 3", World Wide Web
Consortium CR CR-css-fonts-3-20131003, October 2013,
<http://www.w3.org/TR/2013/CR-css-fonts-3-20131003>.
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RFC 8081 The 'font' Top-Level Type February 2017
[ISO.14496-22.2015]
International Organization for Standardization, "Coding of
audio-visual objects Part 22: Open Font Format",
ISO Standard 14496-22, 10 2015,
<http://standards.iso.org/ittf/PubliclyAvailableStandards/
c066391_ISO_IEC_14496-22_2015.zip>.
[W3C.REC-WOFF-20121213]
Kew, J., Leming, T., and E. Blokland, "WOFF File Format
1.0", World Wide Web Consortium Recommendation
REC-WOFF-20121213, December 2012,
<http://www.w3.org/TR/2012/REC-WOFF-20121213>.
[W3C.CR-WOFF2-20150414]
Levantovsky, V. and R. Levien, "WOFF File Format 2.0",
World Wide Web Consortium WD CR-WOFF2-20150414, March
2016, <https://www.w3.org/TR/2016/CR-WOFF2-20160315/>.
5.2. Informative References
[cff-wiki] Wikipedia, "Compact Font Format", November 2016,
<https://en.wikipedia.org/w/
index.php?title=PostScript_fonts&oldid=747740863>.
[opentype-wiki]
Wikipedia, "OpenType", February 2017,
<https://en.wikipedia.org/w/
index.php?title=OpenType&oldid=763528773>.
[truetype-wiki]
Wikipedia, "TrueType", January 2017,
<https://en.wikipedia.org/w/
index.php?title=TrueType&oldid=759367886>.
[svg-wiki] Wikipedia, "Scalable Vector Graphics", February 2017,
<https://en.wikipedia.org/w/
index.php?title=Scalable_Vector_Graphics&oldid=763136508>.
[HTTP-Archive-Trends]
Kuetell, D., "HTTP Archive trend analysis", March 2015,
<http://httparchive.org/trends.php?s=All&minlabel=Nov+15+2
010&maxlabel=Feb+15+2015#perFonts>.
[Font-Media-Type-Analysis]
Kuetell, D., "Web Font Media Type (mime type) Analysis
2015", 2015, <http://goo.gl/zbDhUN>.
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RFC 8081 The 'font' Top-Level Type February 2017
[WG-tlt] W3C, "ACTION-164: Bring widely used top-level type to
w3c-ietf liaison", 2015,
<https://www.w3.org/Fonts/WG/track/actions/164>.
[Media-Type-Registration]
IANA, "Application for a Media Type",
<http://www.iana.org/form/media-types>.
Author's Address
Chris Lilley
W3C
2004 Route des Lucioles
Sophia Antipolis 06902
France
Email: chris@w3.org
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