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The functionalities of manitou-mdx can be extended by writing Perl modules that are hooked to manitou-mdx as plugins. A plugin module may be a self-contained piece of code, but more often it's used as an interface to an external program, such as a spam filter or a converter that extracts text from a complex file format. Also, plugins may use external Perl modules from the CPAN archive or other sources.
A plugin for manitou-mdx is generally just a Perl module .pm file.