Pmcanon accepts an article from the named
file (or standard input if not specified), selects
certain of the header fields,
and performs certain transformations intended to
defeat unintentional mangling by news transport
programs. The resulting article is written to
standard output, and is suitable to have a PGP
signature generated or checked for it.
The output produced consists (in order) of a sorted list,
one per line, of newsgroups; the From:, Subject:,
and Message-ID: lines, and the body of the
article (everything after the first empty line).
Other header lines are discarded.
The body is further processed by deleting all
blank lines, deleting trailing whitespace on
lines, prefixing lines beginning with "--",
"From", "Subject", and a single "." with "- ",
">", ">" and ".", respectively. These
modifications are safe, in that an article which
has already had such modifications will fail to
meet the criterion to have them happen again.
Thus what was used as input when a signature was
generated should still be the same when checked
for validity, even if some of these changes have
happened along the delivery path.