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  2.\" Copyright (c) 2019 Ted Unangst
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 16.Dd $Mdocdate$
 17.Dt HFCS 1
 18.Os
 19.Sh NAME
 20.Nm hfcs
 21.Nd honk filtering and censorship system
 22.Sh DESCRIPTION
 23The honk filtering and censorship system,
 24.Nm hfcs ,
 25controls what messages are seen and how they are presented to the user.
 26Filter rules are based on a series of matches and actions.
 27It is accessed via the
 28.Pa filters
 29menu item.
 30.Pp
 31Each filter has an optional
 32.Ar name
 33and
 34.Ar notes
 35for user defined purposes.
 36.Pp
 37The following match types are possible.
 38All nonempty criteria must match.
 39.Bl -tag -width include-audience
 40.It Ar who
 41Match an actor or domain name.
 42Matches against
 43.Fa Ar actor
 44property.
 45.It Ar include audience
 46Previous match is applied against
 47.It Ar only unknowns
 48Previous (domain) match is applied only to unknown actors.
 49.It Ar text
 50Regular expression match against the post
 51.Fa content .
 52The special value of "." will match any post with a summary only.
 53.It Ar is reply
 54A reply to another post.
 55.It Ar is announce
 56Is announced (shared).
 57.It Ar announce of
 58Limit prevous match to only specified actor or domain name.
 59.El
 60.Pp
 61The following actions may be applied.
 62Multiple actions may be applied, but some are subsumed by others.
 63.Bl -tag -width tenletters
 64.It Ar reject
 65Reject this message entirely.
 66.It Ar skip media
 67Don't include images or attachments.
 68.It Ar hide
 69Remove this message from most feeds.
 70.It Ar collapse
 71Show only a short summary with click to view content.
 72.It Ar rewrite
 73Rewrite message content, using
 74.Ar replace
 75replacement text.
 76.El
 77.Pp
 78The
 79.Ar text
 80and
 81.Ar rewrite
 82fields are case insensitive word anchored regular expressions.
 83Specifically, an argument
 84.Ql re
 85will be automatically rewritten as
 86.Ql \\\b(?i:re)\\\b .
 87The
 88.Ar replace
 89text may refer to submatches using $1, etc.
 90.Pp
 91A post marked sensitive that does not otherwise contain a summary will
 92have an invisible summary of
 93.Dq unspecified horror
 94that can be matched against and will appear if the post is collapsed.
 95.Pp
 96An optional expiration may be specified as a duration.
 97XdYhZm for X days, Y hours, and Z minutes.
 98.Sh EXAMPLES
 99A rudimentary spam filter may be constructed with where set to mastodon.social,
100checking the only unknowns option, with an action of reject.
101.Sh SEE ALSO
102.Xr honk 1
103.Sh CAVEATS
104Not seeing is not erasing.