This is used to add support for parsing documents with mime types other than text/plain and text/html. It can be done via external parser (which must provide output in plain or html text) or just by substituting mime type so indexer will understand it.
from_mime and to_mime are standard mime types to_mime is either text/plain or text/html
Optional charset parameter used to change charset if needed
Command line may have $1 parameter which stands for temporary file name. Some parsers can not operate on stdin, so indexer creates temporary file for parser and it's name passed instead of $1. Take a look into documentation for other parser types and parsers usage explanation.
Mime application/msword "text/plain; charset=cp1251" "catdoc $1" Mime application/x-troff-man text/plain "deroff" Mime text/x-postscript text/plain "ps2ascii" Mime application/pdf text/plain "pdftotext $1 -" Mime application/vnd.ms-excel text/plain "xls2csv $1" Mime "text/rtf*" text/html "rthc --use-stdout $1 2>/dev/null"