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+<!-- go/cmark -->
+<!--* freshness: {owner: 'lndmrk' reviewed: '2022-06-23'} *-->
+
+# Field trials
+
+WebRTC provides some means to alter its default behavior during run-time,
+colloquially known as *field trials*. This is foremost used for A/B testing new
+features and are related to
+[Chromium field trials](https://chromium.googlesource.com/chromium/src/+/main/testing/variations/README.md)
+to facilitate interoperability.
+
+A field trial consist of a key-value pair of strings. By convention, the field
+trial key is prefixed with `WebRTC-` and each word is capitalized without
+spaces. Sometimes the key is further subdivided into a category, for example,
+`WebRTC-MyCategory-MyExperiment`. The field trial value is an opaque string and
+it is up to the author to define what it represents. There are
+[helper functions](https://webrtc.googlesource.com/src/+/refs/heads/main/api/field_trials_view.h)
+to use a field trial as a boolean, with the string `Enabled` representing true
+and `Disabled` representing false. You can also use
+[field trial parameters](https://webrtc.googlesource.com/src/+/refs/heads/main/rtc_base/experiments/field_trial_parser.h)
+if you wish to encode more elaborate data types.
+
+The set of field trials can be instantiated from a single string with the format
+`<key-1>/<value-1>/<key-2>/<value-2>/`. Note the final `/` at the end! In
+Chromium you can launch with the `--force-fieldtrials` flag to instantiate field
+trials this way, for example:
+
+```
+--force-fieldtrials="WebRTC-Foo/Enabled/WebRTC-Bar/Disabled/"
+```
+
+## Policy
+
+The policy for field trials is:
+
+-   A field trial should only be used to test out new code or parameters for a
+    limited time period. It should not be used for configuring persistent
+    behavior.
+-   The field trial must have an end date. The end date may be pushed back if
+    necessary, but should not be pushed back indefinitely.
+-   A field trial must be associated with a bug that
+    -   reserves the field trial key,
+    -   is open,
+    -   is assigned to an owner, and
+    -   has the end date specified.