itrans makes use of an IFM file — indian language font metric file, which is a ASCII file containing descriptions on how to generate the indian language characters from the basic characters available in the font.
Sidenote: This IFM file format is an itrans specific concept, it allows all character composition directives to be loaded in at runtime, making it easy to support many different indian languages. The IFM file is an ASCII file, and all the lines are in a format that the Adobe AFM file specification regards as a comment. Thus, in the future, when all PostScript RIPs really understand the composite character definitions, it may be possible to merge in the IFM file into the AFM file. See the technical reference manual, tech.tex, if you need more complete information regarding the IFM file format.
For example, the IFM file dvnc.ifm contains the descriptions on printing devanagari characters using the devnac.ps devanagari PostScript font, while wntml.ifm contains the descriptions necessary to print all tamil characters, based on the wntml.mf Metafont description.
itrans scans through the input text, and copies everything to
the output unchanged, except for portions between marker words,
such as \char92marathi and \char92endmarathi.
Some eight–ten different marker words are available, see the Appendix A
for more information.
All english text between these words is mapped into indian language characters,
based on the transliteration map.
At the beginning of the input file, the user has to specify the IFM file, and the name of the TEX or PostScript command that changes the font to the indian language font. For example, if the IFM file is named dvnc.ifm, and the font is available through the \devnf TEX command, the following two lines should be present in the input file:
\char92marathiifm=dvnc
This also assumes the user will be using the markers \char92marathi and \char92endmarathi, see
Appendix A for all the other language markers and commands.
Once the above initialization is made, the \char92marathi marker then specifies the
beginning of the marathi transliterated text, and makes use of the
specified IFM file (dvnc.ifm).
At that point, itrans also outputs the font
changing command (\devnf) specified in the \marathifont
directive.
Note that both the TEX interface and the Dumb interface follow identical input text requirements. For further examples, see the sample documents provided. All TEX transliterated files have been given the file extension .itx. All Dumb Input transliterated files have been given the file extension .ips.