X logical font description

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X logical font description (XLFD) is a font standard used by the X Window System and first published in 1988.^[1] Modern X software typically relies on the newer Fontconfig system instead, but XLFDs are still supported in current X window implementations for compatibility with legacy software.

XLFD is intended to support:

• unique, descriptive font names that support simple pattern matching
• multiple font vendors, arbitrary character sets, and encodings
• naming and instancing of scalable and polymorphic fonts
• transformations and subsetting of fonts
• independence of X server and operating or file system implementations
• arbitrarily complex font matching or substitution
• extensibility

One prominent XLFD convention is to refer to individual fonts including any variations using their unique FontName. It comprises a sequence of fourteen hyphen-prefixed, X-registered fields:

1. FOUNDRY: Type foundry - vendor or supplier of this font
2. FAMILY_NAME: Typeface family
3. WEIGHT_NAME: Weight of type
4. SLANT: Slant (upright, italic, oblique, reverse italic, reverse oblique, or "other")
5. SETWIDTH_NAME: Proportionate width (e.g. normal, condensed, narrow, expanded/double-wide)
6. ADD_STYLE_NAME: Additional style (e.g. (Sans) Serif, Informal, Decorated)
7. PIXEL_SIZE: Size of characters, in pixels; 0 (Zero) means a scalable font
8. POINT_SIZE: Size of characters, in tenths of points
9. RESOLUTION_X: Horizontal resolution in dots per inch (DPI), for which the font was designed
10. RESOLUTION_Y: Vertical resolution, in DPI
11. SPACING: monospaced, proportional, or "character cell"
12. AVERAGE_WIDTH: Average width of characters of this font; 0 means scalable font
13. CHARSET_REGISTRY: Registry defining this character set
14. CHARSET_ENCODING: Registry's character encoding scheme for this set

The following sample is for a 75-dpi, 12-point, Charter font:

-bitstream-charter-medium-r-normal--12-120-75-75-p-68-iso8859-1[65 70 80_90] 

(which also tells the font source that the client is interested only in characters 65, 70, and 80-90.)

• Jim Flowers; Stephen Gildea (1994) [1988 (first version, based on copyright)]. "X Logical Font Description Conventions" (PDF). Digital Equipment Corporation. X Consortium. Retrieved 2015-11-22.
• Mansfield, Niall (1994) [1992]. "System Administration". The Joy of X - An overview of the X Window System. Cambridge: Addison-Wesley. pp. 266–267. ISBN 0-201-56512-9.

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