Sometimes, a user is confronted with certain content they don't want to read,
e.g. on topics the user is not interested in or articles written by certain people.
In Usenet, such functionality within software is traditionally called a "killfile",
i.e. based on the content of this "killfile", articles that match certain conditions
do not get displayed and are not presented to the user at all.

In Newsboat, such a "killfile" can be implemented on a per-article basis via
the configuration file. The most important configuration command for this
is <<ignore-article,`ignore-article`>>:

	ignore-article "https://synflood.at/blog/index.php?/feeds/index.rss2" "title =~ \"newsboat\""
	ignore-article "regex:https?://nitter.net/.*" "title =~ \"^RT by\""
	ignore-article "*" "title =~ \"Gentoo\""

It takes two parameters. The first one is either:

 - The URL of a feed.
 - A pattern prefixed with `regex:`. The pattern must be
 a https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/basedefs/V1_chap09.html[POSIX
 extended regular expression], which will be matched case-insensitive.
 - `"*"` to match any feed (asterisk is _not_ a pattern, glob or regex—we simply
 reserve it to mean "all feeds").

The second argument is <<_filter_language,a filter expression>> for an article,
probably <<_using_double_quotes,in double quotes to preserve spaces inside>>. If
Newsboat hits an article in the specified RSS feed that matches the specified
filter expression, then this article is ignored and never presented to the user.
The configuration itself can contain as many <<ignore-article,`ignore-article`>>
commands as desired.

You can also specify the way an article is ignored. There are
two ways available:

 - During download: articles are ignored when a feed is downloaded and parsed,
   and thus won't be written to the local cache.
 - During display: articles are downloaded and written to the local cache, but
   are ignored when a feed is displayed.

Both modes have their advantages and disadvantages: while the download ignore
mode saves some storage, you cannot simply "undo" the ignore by removing it
from the configuration file: if an ignored article has already vanished from a
feed, it won't reappear. On the other hand, the display ignore mode requires
some more space, but has the advantage that an ignore can be "undone" by
removing the ignore-article configuration command from the configuration.

The default ignore mode is `"download"`. You can set the <<ignore-mode,`ignore-mode`>> in the
configuration file:

	ignore-mode "display"

