-# This script reformats mail drafts according to a given template. The
-# template may be specified on the command line, but mailplate can also use
-# control information from the template files to automatically select an
-# appropriate template (--auto). A selection menu feature is planned (--menu).
-#
-# Applying a template means obtainined select data from an existing mail
-# message (unless --new is specified) and to fill it into appropriate slots in
-# the template. Messages are processed in three parts: headers, body, and
-# signature.
-#
-# The template can define two types of headers: mandatory and preservatory.
-# Mandatory headers take precedence over headers in the existing message and
-# thus overwrite them. Preservatory headers instruct mailplate to port their
-# data from the existing mail message. Headers in the existing message but not
-# defined in the template are dropped, unless --keep-unknown is given.
-#
-# Body and signature are separated by '-- '. If this sentinel is not found,
-# no signature is extracted.
-#
-# Templates can be interpolated and data filled into slots. Helper slots are
-# filled with the output of helper commands (which must be defined in the
-# configuration), environment variable slots are just that, and mail variable
-# slots can be filled with data obtained by running regexps or commands over
-# the message.
-#
-# This script can be run in multiple ways:
-#
-# As a filter, it applies a template to data from stdin and writes the result
-# to stdout.
-#
-# Given a file, it modifies the file, unless it cannot write to the file, in
-# which case it writes to stdout.
-#
-# When --editor is passed, the script spawns sensible-editor on the result. It
-# may thus be used as the editor for your mail user agent.