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+# Filters
+
+Filters are a very powerful and flexible tool which may significantly ease the
+task of extracting useful information from the sea of data that is RSS feeds.
+Filters are applied to articles based on [regular
+expression](http://en.wikipedia.org/wiki/Regular_expression) matches against
+specified fields. After the match had been found, configured actions are taken.
+Matching is case-insensitive,
+[PCRE](http://php.net/manual/en/reference.pcre.pattern.syntax.php) pattern
+syntax is used.
+
+!!! notice
+
+    Filter test dialog may not give entirely accurate results, especially for
+    complex filters. It is suggested to test filters using ``Feed debugger`` (hotkey `f D`) if you
+    feel that some filter is somehow misfiring on a specific feed.
+
+### Load order
+
+Filters are loaded in user-specified order and applied sequentially. It is
+possible to reorder filters using drag and drop. If no manual sorting is
+specified, filters are sorted alphabetically according to user configured
+caption. If no caption is specified for any filter, loading order is not
+guaranteed.
+
+### Filter objects
+
+Each filter object may contain an arbitrary amount of regular expression rules
+and actions. Each expression may have inverse flag set, which inverts matching
+result. On top of that, filter may also have an inverse flag, which inverts the
+final matching.
+
+- Filter object may be configured to successfully match when either one or
+all rules match.
+- Regular expressions may be matched against several article fields, such
+as, title, content, author, etc.
+- Do not include delimiters (e.g. <code>/</code>) when writing regular
+expressions.
+
+### Matching articles and applying actions
+
+Filter matching is performed during feed processing.
+
+!!! notice
+
+    Some actions may be applied only when the article is initially imported from the
+    feed. Other actions may be applied every time article is seen in the originating
+    feed. It is suggested to only rely on filters applying to articles imported
+    after the filter had been created - they will not retroactively apply to your
+    article database.
+
+Several actions are available:
+
+!!! warning
+
+    Filters may not apply actions conditionally based on previous filters. All actions for an article are applied together, once.
+
+1. ``Delete article`` - do not import article from the feed, does not
+actually delete anything from the database
+2. ``Mark as read`` - imports article automatically marked as read
+3. ``Set starred`` - sets article starred automatically on import
+4. ``Assign tags`` - assigns a comma-separated list of custom tags on import
+5. ``Publish article`` - sets article published automatically on import
+6. ``Modify score`` ([Scoring](Scoring.md)) - modifies article overall score based on
+the parameter, a signed integer number. Final article score is calculated after all filters had been applied and is a sum of all matched scoring actions.
+7. ``Assign label`` - assigns specified label to the article on import
+8. ``Stop / Do nothing`` - stops further filter processing for this article, no following filters will be checked nor rules applied.
+9. ``Invoke plugin`` - runs a plugin action when filter is matched
+10. ``Ignore tags`` - a comma-separated list of tags which will be skipped on article import
+
+After all matching filters had been computed for the article, it is either
+imported with modifications as specified by the rules, or dropped if `Delete
+article` action has been found.