diff --git a/content/_index.md b/content/_index.md
index 62e2ef85..06d867e8 100644
--- a/content/_index.md
+++ b/content/_index.md
@@ -99,6 +99,22 @@ services - be that for instant messages, VoIP call setups, or any other
 objects that need to be reliably and persistently pushed from A to B in
 an interoperable and federated manner.
 
+### Bindingness of requirements
+
+As a standards document, the Matrix Spec needs to signify the bindingness of the
+individual features, APIs, procedures, or other requirements it describes.
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
+"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" across all parts of the
+specification are to be interpreted as described in
+[RFC 2119](https://datatracker.ietf.org/doc/html/rfc2119).
+
+Some entire sections of the specification might be optional depending on the
+circumstances, for example the
+[modules of the client-server API](/client-server-api/#modules) apply depending
+on the use case. The bindingness of the above key words appearing in such a
+section is only relevant if the section itself is applicable.
+
 ### Spec Change Proposals
 
 To propose a change to the Matrix Spec, see the explanations at