Printing filter is a perl subroutine which takes one or more data sections and produces an alternative printable representation of them.

In order to be available to the user, a filter subroutine has to be defined in the package Filters. It gets an array of arguments, where each input section is represented by two adjacent elements: the section name as a string, and the section contents as an array reference (it is always array, regardless the number of lines in the section.) Since it is the reference to the original data, the filter should better avoid changing them.

The return value must be in the same form: a list of alternating section names and array references. The length of the output list and the actual names of the output sections may, however, differ from the input.

The package Filters contains a global hash %description, which serves as a documentation source. The keys in the hash should be identical to the filter names.