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<h1 id="implementing-experimental-features-in-synapse"><a class="header" href="#implementing-experimental-features-in-synapse">Implementing experimental features in Synapse</a></h1>
<p>It can be desirable to implement &quot;experimental&quot; features which are disabled by
default and must be explicitly enabled via the Synapse configuration. This is
applicable for features which:</p>
<ul>
<li>Are unstable in the Matrix spec (e.g. those defined by an MSC that has not yet been merged).</li>
<li>Developers are not confident in their use by general Synapse administrators/users
(e.g. a feature is incomplete, buggy, performs poorly, or needs further testing).</li>
</ul>
<p>Note that this only really applies to features which are expected to be desirable
to a broad audience. The <a href="../modules/index.html">module infrastructure</a> should
instead be investigated for non-standard features.</p>
<p>Guarding experimental features behind configuration flags should help with some
of the following scenarios:</p>
<ul>
<li>Ensure that clients do not assume that unstable features exist (failing
gracefully if they do not).</li>
<li>Unstable features do not become de-facto standards and can be removed
aggressively (since only those who have opted-in will be affected).</li>
<li>Ease finding the implementation of unstable features in Synapse (for future
removal or stabilization).</li>
<li>Ease testing a feature (or removal of feature) due to enabling/disabling without
code changes. It also becomes possible to ask for wider testing, if desired.</li>
</ul>
<p>Experimental configuration flags should be disabled by default (requiring Synapse
administrators to explicitly opt-in), although there are situations where it makes
sense (from a product point-of-view) to enable features by default. This is
expected and not an issue.</p>
<p>It is not a requirement for experimental features to be behind a configuration flag,
but one should be used if unsure.</p>
<p>New experimental configuration flags should be added under the <code>experimental</code>
configuration key (see the <code>synapse.config.experimental</code> file) and either explain
(briefly) what is being enabled, or include the MSC number.</p>
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