diff --git a/index.bs b/index.bs
index e14041e..b4d0718 100644
--- a/index.bs
+++ b/index.bs
@@ -243,6 +243,9 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
           <li>
             If <code>keySystemConfiguration</code> [=map/exists=]:
             <ol>
+              <li>
+                The <code>type</code> MUST be {{media-source}} or {{file}}.
+              </li>
               <li>
                 If <code>keySystemConfiguration.audio</code> [=map/exists=],
                 <code>audio</code> MUST also [=map/exist=].
@@ -402,6 +405,11 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
             If {{VideoConfiguration/framerate}} is not finite or is not greater
             than 0, return <code>false</code> and abort these steps.
           </li>
+          <li>
+            If an optional member is specified for a {{MediaDecodingType}} or
+            {{MediaEncodingType}} to which it's not applicable, return
+            <code>false</code> and abort these steps. See applicability rules
+            in the member definitions below.
           <li>
             Return <code>true</code>.
           </li>
@@ -449,7 +457,9 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
         member represents that the video track includes the specified HDR
         metadata type, which the UA needs to be capable of interpreting for tone
         mapping the HDR content to a color volume and luminance of the output
-        device. Valid inputs are defined by {{HdrMetadataType}}.
+        device. Valid inputs are defined by {{HdrMetadataType}}. hdrMetadataType is
+        only applicable to {{MediaDecodingConfiguration}} for types {{media-source}}
+        and {{file}}.
       </p>
 
       <p>
@@ -461,7 +471,9 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
         to render the appropriate color, or something close enough. If the
         attached output device does not support the specified color, the UA
         needs to be capable of mapping the specified color to a color supported
-        by the output device. Valid inputs are defined by {{ColorGamut}}.
+        by the output device. Valid inputs are defined by {{ColorGamut}}. colorGamut
+        is only applicable to {{MediaDecodingConfiguration}} for types
+        {{media-source}} and {{file}}.
       </p>
 
       <p>
@@ -471,7 +483,8 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
         electro-optical algorithm supported by the rendering capabilities of a
         user agent, independent of the display, to map the source colors in the
         decoded media into the colors to be displayed. Valid inputs are defined
-        by {{TransferFunction}}.
+        by {{TransferFunction}}. transferFunction is only applicable to
+        {{MediaDecodingConfiguration}} for types {{media-source}} and {{file}}.
       </p>
 
       <p>
@@ -480,7 +493,7 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
         absent, the implementer defined default mode for this {{contentType}} is
         assumed (i.e., the mode you get if you don't specify one via
         {{RTCRtpSender/setParameters()}}). scalabilityMode is only applicable
-        to the {{MediaEncodingType}} {{MediaEncodingType/webrtc}}.
+        to {{MediaEncodingConfiguration}} for type {{MediaEncodingType/webrtc}}.
       </p>
 
       <p>
@@ -492,7 +505,8 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
         {{scalabilityMode}} in the sense that streams encoded with modes using
         spatial scalability (e.g. "L2T1") can only be decoded if
         spatialScalability is supported. spatialScalability is only applicable
-        to {{MediaDecodingConfiguration}}.
+        to {{MediaDecodingConfiguration}} for types {{media-source}}, {{file}},
+        and {{MediaDecodingType/webrtc}}.
       </p>
     </section>
 
@@ -638,7 +652,10 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
 
       <p>
         The <dfn for='AudioConfiguration' dict-member>channels</dfn> member
-        represents the audio channels used by the audio track.
+        represents the audio channels used by the audio track. channels is only
+        applicable to the decoding types {{media-source}}, {{file}}, and
+        {{MediaDecodingType/webrtc}} and the encoding type
+        {{MediaEncodingType/webrtc}}.
       </p>
 
       <p class='issue'>
@@ -657,7 +674,10 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
       <p>
         The <dfn for='AudioConfiguration' dict-member>samplerate</dfn>
         represents the samplerate of the audio track in. The samplerate is the
-        number of samples of audio carried per second.
+        number of samples of audio carried per second. samplerate is only
+        applicable to the decoding types {{media-source}}, {{file}}, and
+        {{MediaDecodingType/webrtc}} and the encoding type
+        {{MediaEncodingType/webrtc}}.
       </p>
 
       <p class='note'>
@@ -677,7 +697,8 @@ spec: secure-contexts; urlPrefix: https://www.w3.org/TR/secure-contexts/
         the user agent SHOULD only report this configuration as
         {{MediaCapabilitiesInfo/supported}} if it can support spatial
         rendering *for the current audio output device* without failing back to a
-        non-spatial mix of the stream.
+        non-spatial mix of the stream. spatialRendering is only applicable to
+        {{MediaDecodingConfiguration}} for types {{media-source}} and {{file}}.
       </p>
     </section>
   </section>