CUPS autoconstructs all possible filtering chain paths for any given
MIME type and every printer installed. But how does it decide in
favor of or against a specific alternative? (There may be cases
where there is a choice of two or more possible filtering chains for
the same target printer.) Simple. You may have noticed the figures in
the third column of the mime.convs file. They represent virtual costs
assigned to this filter. Every possible filtering chain will sum up to
a total “filter cost.” CUPS decides for the most “inexpensive” route.