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*** Defining fontsets.

Emacs does not use any fontset by default. Its default font is still chosen as in previous versions. You can tell Emacs to use a fontset with the `-fn' option or the `Font' X resource.

Emacs creates a standard fontset automatically according to the value of standard-fontset-spec. This fontset's short name is `fontset-standard'. Bold, italic, and bold-italic variants of the standard fontset are created automatically.

If you specify a default ASCII font with the `Font' resource or `-fn' argument, a fontset is generated from it. This works by replacing the FOUNDARY, FAMILY, ADD_STYLE, and AVERAGE_WIDTH fields of the font name with `*' then using this to specify a fontset. This fontset's short name is `fontset-startup'.

Emacs checks resources of the form Fontset-N where N is 0, 1, 2...

The resource value should have this form:
FONTSET-NAME should have the form of a standard X font name, except:
The construct CHARSET-NAME:FONT-NAME can be repeated any number of times; each time specifies the font for one character set. CHARSET-NAME should be the name name of a character set, and FONT-NAME should specify an actual font to use for that character set.

Each of these fontsets has an alias which is made from the last two font name fields, CHARSET_REGISTRY and CHARSET_ENCODING. You can refer to the fontset by that alias or by its full name.

For any character sets that you don't mention, Emacs tries to choose a font by substituting into FONTSET-NAME. For instance, with the following resource, Emacs*Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24

the font for ASCII is generated as below:
Here is the substitution rule:
Change CHARSET_REGISTRY and CHARSET_ENCODING to that of the charset defined in the variable x-charset-registries. For instance, ASCII has the entry (ascii . "ISO8859-1") in this variable. Then, reduce sequences of wild cards -*-...-*- with a single wildcard -*-. (This is to prevent use of auto-scaled fonts.)
The function which processes the fontset resource value to create the fontset is called create-fontset-from-fontset-spec. You can also call that function explicitly to create a fontset.

With the X resource Emacs.Font, you can specify a fontset name just like an actual font name. But be careful not to specify a fontset name in a wildcard resource like Emacs*Font--that tries to specify the fontset for other purposes including menus, and they cannot handle fontsets.