- Fallback font
A fallback font is a reserve typeface containing symbols for as many
Unicode characters as possible. When a display system encounters a character which is not part of the repertoire of any of the other available fonts, a symbol from a fallback font is used instead. Typically, a fallback font will contain symbols representative of the various types of Unicode characters. The use of a fallback font is suggested in "The Unicode Standard ".Systems that do not offer a fallback font typically display black or white rectangles,
question mark s, or nothing at all in place of missing characters. Symbols in a fallback font can contain annotations such as the relevant Unicode block and the script system used.Apple's "LastResort" font
LastResort is a
Mac OS font that is invisible to the end user, but is used by the system to display glyphs that are not available in any other font. The symbols provided by LastResort place glyphs into categories based on their location in theUnicode system and provide a hint to the user about which font or script is required to view the unavailable characters. The symbols provided by LastResort are square with rounded corners with a bold outline. In the left and right sides of the outline, theUnicode range that the character belongs to is given using hexadecimal digits. Top and bottom are used for one or two descriptions of theUnicode block . A symbol representative of the block is centered inside the square.Apple's "LastResort" font was first included in
Mac OS 8.5 in 1998, for the benefit of applications usingApple Type Services for Unicode Imaging (ATSUI). It is also used inMac OS X . In 2001, for the second release of OS X, the Last Resort font design was revised to include the border text and was re-digitized, and extended byMichael Everson ofEvertype , who continues to update it with each new release of Unicode. Apple has now made the Last Resort font available for free download from the Unicode website.One prototypic glyph per Unicode block is used because the total number of Unicode characters greatly exceeds the address space of an sfnt (TrueType and OpenType) font structure, which has a 16-bit glyph index that can store a maximum of only 65,536 glyphs. Unicode has now over 100,000 defined characters, with a potential address space of over one million characters - over 15 times the sfnt size limit. Using this one-glyph-per-block generalization, the Last Resort font is still capable of showing a glyph for every byte in Unicode. The Last Resort mechanism will therefore not break as Unicode continues to grow and the
Basic Multilingual Plane (BMP) and surrogate planes fill up further.The "Unicode BMP Fallback" font
0 0The Unicode BMP Fallback font is a
2 0Unicode font containing a glyph for every character in theBasic multilingual plane . Each glyph consists of a box containing the four hex digits corresponding to the Unicode value. The example to the left is a mock-up of the glyph for aspace character (U+0020).The font was created for
debugging purposes.ee also
*
Fonts on Macintosh
*Unicode References
* Apple Computer (
November 2 ,2002 ). [http://developer.apple.com/fonts/LastResortFont/ Apple's "LastResort" font web site] . Retrieved2004 -11-02 .
* The Unicode Consortium (March 30 ,2004 ). [http://www.unicode.org/versions/Unicode4.0.1/ The Unicode Standard, 4.0.1] . Retrieved2004 -11-02 .
* [http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&item_id=UnicodeBMPFallbackFont Description] of the Unicode BMP fallback font atSIL International External links
* [http://www.unicode.org/policies/lastresortfont_eula.html Last Resort Font download]
* [http://developer.apple.com/textfonts/LastResortFont/ Apple Computer on LastResort]
* [http://www.mail-archive.com/unicode@unicode.org/msg18168.html brief discussion of Last Resort by Michael Everson]
* [http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&item_id=UnicodeBMPFallbackFont SIL International's Unicode BMP Fallback Font] — Free fallback font
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