Replace misuses of 'plaintext' with 'cleartext' and clarify spoiler docs (#1306)

changelogs/client_server/newsfragments/1306.clarification

@@ -0,0 +1 @@
+Various clarifications throughout the specification.

content/client-server-api/_index.md

@@ -1945,14 +1945,14 @@ parent event, for example.
 {{% /boxes/note %}}
 
 To allow the server to aggregate and find child events for a parent, the `m.relates_to`
-key of an event MUST be included in the plaintext copy of the event. It cannot be
+key of an event MUST be included in the cleartext portion of the event. It cannot be
 exclusively recorded in the encrypted payload as the server cannot decrypt the event
 for processing.
 
 {{% boxes/warning %}}
 If an encrypted event contains an `m.relates_to` in its payload, it should be
-ignored and instead favour the plaintext `m.relates_to` copy (including when there
+ignored and instead favour the cleartext `m.relates_to` copy (including when there
-is no plaintext copy). This is to ensure the client's behaviour matches the server's
+is no cleartext copy). This is to ensure the client's behaviour matches the server's
 capability to handle relationships.
 {{% /boxes/warning %}}
 

content/client-server-api/modules/instant_messaging.md

@@ -327,11 +327,11 @@ If a reason were to be supplied, it would look like:
 }
 ```
 
-When sending a spoiler, clients SHOULD provide the plain text fallback in the `body`
+When sending a spoiler, clients SHOULD provide the fallback in the `body` as shown above
-as shown above (including the reason). The fallback SHOULD omit the spoiler text verbatim
+(including the reason). The fallback SHOULD NOT include the text containing spoilers since
-since `body` might show up in text-only clients or in notifications. To prevent spoilers
+`body` might show up in text-only clients or in notifications. To prevent spoilers showing up in
-showing up in such situations, clients are strongly encouraged to first upload the plaintext
+such situations, clients are strongly encouraged to first upload the text containing spoilers
-to the media repository then reference the MXC URI in a markdown-style link, as shown above.
+to the media repository, then reference the MXC URI in a markdown-style link, as shown above.
 
 Clients SHOULD render spoilers differently with some sort of disclosure. For example, the
 client could blur the actual text and ask the user to click on it for it to be revealed.

content/identity-service-api.md

@@ -280,7 +280,7 @@ request.
 
 #### `none`
 
-This algorithm performs plaintext lookups on the identity server.
+This algorithm performs cleartext lookups on the identity server.
 Typically this algorithm should not be used due to the security concerns
 of unhashed identifiers, however some scenarios (such as LDAP-backed
 identity servers) prevent the use of hashed identifiers. Identity