X logical font description
# X logical font description

X logical font description (XLFD) is a font standard used by the X Window System. 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:

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

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

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

