README: describe filter syntax

1 files changed, 9 insertions, 1 deletions

diff --git a/README.md b/README.md
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@@ -10,7 +10,15 @@ Open a video. Press `space` to start or stop video playback. Seek with `←` and
 
 To add a new event, press the key for the corresponding tag and fill out event details. Custom tags can be defined as a JSON array and loaded at runtime. See `tags.json` for the built‐in example showcasing all supported field types.
 
-Events for `video.mp4` are saved in JSON format in the file `video.mp4.events`. Saved file includes tag definitions, which are loaded automatically when the file is opened. Event timestamps are stored with millisecond precision.
+Events for `video.mp4` are saved in JSON format to the file `video.mp4.events`. The saved file includes tag definitions, which are loaded automatically when the video is opened. Event timestamps are stored with millisecond precision.
+
+### Filter
+
+Input space‐separated search strings to select a subset of events. Selected events must match each string, either as the tag name or a field value. Tags are matched from the beginning, so `p` will select events tagged `pass` and `penalty`.
+
+Text and enum fields match when they contain the given search string. Prefixing the string with `=` specifies a complete match. The string `2` thus matches values `123`, `2` and `22`, while `=2` only matches `2`. A boolean field matches when it’s value is true and it’s name starts with the search string. Prefixing the string with `!` inverts the match.
+
+Finally, a search string can be prefixed with a (prefix of) field name, as in `play:2`. This selects events with a field named `player` whose value matches `2` as above. This can be combined with the `!` and `=` operators, as in `pass:!success`.
 
 ## Compiling