Support s tags for strikethrough for Matrix v1.10

src/HtmlUtils.tsx

@@ -124,6 +124,7 @@ const topicSanitizeHtmlParams: IExtendedSanitizeOptions = {
     allowedTags: [
         "font", // custom to matrix for IRC-style font coloring
         "del", // for markdown
+        "s",
         "a",
         "sup",
         "sub",

src/Linkify.tsx

@@ -147,8 +147,10 @@ export const transformTags: NonNullable<IExtendedSanitizeOptions["transformTags"
 
 export const sanitizeHtmlParams: IExtendedSanitizeOptions = {
     allowedTags: [
+        // These tags are suggested by the spec https://spec.matrix.org/v1.10/client-server-api/#mroommessage-msgtypes
         "font", // custom to matrix for IRC-style font coloring
         "del", // for markdown
+        "s",
         "h1",
         "h2",
         "h3",

src/Markdown.ts

@@ -22,7 +22,7 @@ import { logger } from "matrix-js-sdk/src/logger";
 
 import { linkify } from "./linkify-matrix";
 
-const ALLOWED_HTML_TAGS = ["sub", "sup", "del", "u", "br", "br/"];
+const ALLOWED_HTML_TAGS = ["sub", "sup", "del", "s", "u", "br", "br/"];
 
 // These types of node are definitely text
 const TEXT_NODES = ["text", "softbreak", "linebreak", "paragraph", "document"];

src/editor/deserialize.ts

@@ -195,6 +195,8 @@ function parseNode(n: Node, pc: PartCreator, opts: IParseOptions, mkListItem?: (
                     return [pc.plain("**"), ...parseChildren(n, pc, opts), pc.plain("**")];
                 case "DEL":
                     return [pc.plain("<del>"), ...parseChildren(n, pc, opts), pc.plain("</del>")];
+                case "S":
+                    return [pc.plain("<s>"), ...parseChildren(n, pc, opts), pc.plain("</s>")];
                 case "SUB":
                     return [pc.plain("<sub>"), ...parseChildren(n, pc, opts), pc.plain("</sub>")];
                 case "SUP":