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The res, unitwidth, fonts, and sizes lines are compulsory. Other commands are ignored by troff but may be used by postprocessors to store arbitrary information about the device in the DESC file.
Here a list of obsolete keywords which are recognized by groff but completely ignored: spare1, spare2, biggestfont.
Other commands are ignored by troff but may be used by postprocessors to store arbitrary information about the font in the font file.
The first section can contain comments which start with the # character and extend to the end of a line.
The second section contains one or two subsections. It must contain a charset subsection and it may also contain a kernpairs subsection. These subsections can appear in any order. Each subsection starts with a word on a line by itself.
The word charset starts the charset subsection. The charset line is followed by a sequence of lines. Each line gives information for one character. A line comprises a number of fields separated by blanks or tabs. The format is
name identifies the character: if name is a single character c then it corresponds to the groff input character c; if it is of the form [rs]c where c is a single character, then it corresponds to the special character [rs][c]; otherwise it corresponds to the groff input character [rs][name]. If it is exactly two characters xx it can be entered as [rs](xx. Note that single-letter special characters can't be accessed as [rs]c; the only exception is `[rs]-' which is identical to `[rs][-]'. The name --- is special and indicates that the character is unnamed; such characters can only be used by means of the [rs]N escape sequence in troff.
Groff supports eight-bit characters; however some utilities have difficulties with eight-bit characters. For this reason, there is a convention that the name charn is equivalent to the single character whose code is n. For example, char163 would be equivalent to the character with code 163 which is the pounds sterling sign in ISO Latin-1.
The type field gives the character type:
The code field gives the code which the postprocessor uses to print the character. The character can also be input to groff using this code by means of the [rs]N escape sequence. The code can be any integer. If it starts with a 0 it will be interpreted as octal; if it starts with 0x or 0X it will be intepreted as hexadecimal. Note, however, that the [rs]N escape sequence only accepts a decimal integer.
The entity_name field gives an ascii string identifying the glyph which the postprocessor uses to print the character. This field is optional and has been introduced so that the html device driver can encode its character set. For example, the character `[rs][Po]' is represented as `£' in html 4.0.
Anything on the line after the encoding field resp. after `--' will be ignored.
The metrics field has the form (in one line; it is broken here for the sake of readability):
There must not be any spaces between these subfields. Missing subfields are assumed to be 0. The subfields are all decimal integers. Since there is no associated binary format, these values are not required to fit into a variable of type char as they are in ditroff. The width subfields gives the width of the character. The height subfield gives the height of the character (upwards is positive); if a character does not extend above the baseline, it should be given a zero height, rather than a negative height. The depth subfield gives the depth of the character, that is, the distance below the lowest point below the baseline to which the character extends (downwards is positive); if a character does not extend below above the baseline, it should be given a zero depth, rather than a negative depth. The italic-correction subfield gives the amount of space that should be added after the character when it is immediately to be followed by a character from a roman font. The left-italic-correction subfield gives the amount of space that should be added before the character when it is immediately to be preceded by a character from a roman font. The subscript-correction gives the amount of space that should be added after a character before adding a subscript. This should be less than the italic correction.
A line in the charset section can also have the format
This indicates that name is just another name for the character mentioned in the preceding line.
The word kernpairs starts the kernpairs section. This contains a sequence of lines of the form:
This means that when character c1 appears next to character c2 the space between them should be increased by n. Most entries in kernpairs section will have a negative value for n.
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