diff --git a/lib/shared/markdown.js b/lib/shared/markdown.js
index ad5e361dd..b6286b9fa 100644
--- a/lib/shared/markdown.js
+++ b/lib/shared/markdown.js
@@ -1,272 +1,275 @@
 // @flow
 
 import invariant from 'invariant';
 
 import type { RelativeMemberInfo } from '../types/thread-types';
 import { oldValidUsernameRegexString } from './account-utils';
 
 // simple-markdown types
 export type State = {
   key?: string | number | void,
   inline?: ?boolean,
   [string]: any,
 };
 
 export type Parser = (source: string, state?: ?State) => Array<SingleASTNode>;
 
 export type Capture =
   | (Array<string> & { +index: number, ... })
   | (Array<string> & { +index?: number, ... });
 
 export type SingleASTNode = {
   type: string,
   [string]: any,
 };
 
 export type ASTNode = SingleASTNode | Array<SingleASTNode>;
 
 type UnTypedASTNode = {
   [string]: any,
   ...
 };
 
 type MatchFunction = { regex?: RegExp, ... } & ((
   source: string,
   state: State,
   prevCapture: string,
 ) => ?Capture);
 
 export type ReactElement = React$Element<any>;
 type ReactElements = React$Node;
 
 export type Output<Result> = (node: ASTNode, state?: ?State) => Result;
 
 type ArrayNodeOutput<Result> = (
   node: Array<SingleASTNode>,
   nestedOutput: Output<Result>,
   state: State,
 ) => Result;
 
 type ArrayRule = {
   +react?: ArrayNodeOutput<ReactElements>,
   +html?: ArrayNodeOutput<string>,
   +[string]: ArrayNodeOutput<any>,
 };
 
 type ParseFunction = (
   capture: Capture,
   nestedParse: Parser,
   state: State,
 ) => UnTypedASTNode | ASTNode;
 
 type ParserRule = {
   +order: number,
   +match: MatchFunction,
   +quality?: (capture: Capture, state: State, prevCapture: string) => number,
   +parse: ParseFunction,
   ...
 };
 
 export type ParserRules = {
   +Array?: ArrayRule,
   +[type: string]: ParserRule,
   ...
 };
 
 const paragraphRegex: RegExp = /^((?:[^\n]*)(?:\n|$))/;
 const paragraphStripTrailingNewlineRegex: RegExp = /^([^\n]*)(?:\n|$)/;
 
 const headingRegex: RegExp = /^ *(#{1,6}) ([^\n]+?)#* *(?![^\n])/;
 const headingStripFollowingNewlineRegex: RegExp = /^ *(#{1,6}) ([^\n]+?)#* *(?:\n|$)/;
 
 const fenceRegex: RegExp = /^(`{3,}|~{3,})[^\n]*\n([\s\S]*?\n)\1(?:\n|$)/;
 const fenceStripTrailingNewlineRegex: RegExp = /^(`{3,}|~{3,})[^\n]*\n([\s\S]*?)\n\1(?:\n|$)/;
 
 const codeBlockRegex: RegExp = /^(?: {4}[^\n]*\n*?)+(?!\n* {4}[^\n])(?:\n|$)/;
 const codeBlockStripTrailingNewlineRegex: RegExp = /^((?: {4}[^\n]*\n*?)+)(?!\n* {4}[^\n])(?:\n|$)/;
 
 const urlRegex: RegExp = /^(https?:\/\/[^\s<]+[^<.,:;"')\]\s])/i;
 
 const mentionRegex = new RegExp(`^(@(${oldValidUsernameRegexString}))\\b`);
 
 export type JSONCapture = Array<string> & {
   +json: Object,
   +index?: void,
   ...
 };
 function jsonMatch(source: string): ?JSONCapture {
   if (!source.startsWith('{')) {
     return null;
   }
 
   let jsonString = '';
   let counter = 0;
   for (let i = 0; i < source.length; i++) {
     const char = source[i];
     jsonString += char;
     if (char === '{') {
       counter++;
     } else if (char === '}') {
       counter--;
     }
     if (counter === 0) {
       break;
     }
   }
   if (counter !== 0) {
     return null;
   }
 
   let json;
   try {
     json = JSON.parse(jsonString);
   } catch {
     return null;
   }
   if (!json || typeof json !== 'object') {
     return null;
   }
 
   return { ...([jsonString]: any), json };
 }
 
 function jsonPrint(capture: JSONCapture): string {
   return JSON.stringify(capture.json, null, '  ');
 }
 
 const listRegex = /^( *)([*+-]|\d+\.) ([\s\S]+?)(?:\n{2}|\s*\n*$)/;
 const listItemRegex = /^( *)([*+-]|\d+\.) [^\n]*(?:\n(?!\1(?:[*+-]|\d+\.) )[^\n]*)*(\n|$)/gm;
 const listItemPrefixRegex = /^( *)([*+-]|\d+\.) /;
 const listLookBehindRegex = /(?:^|\n)( *)$/;
 
 function matchList(source: string, state: State): RegExp$matchResult | null {
   if (state.inline) {
     return null;
   }
   const prevCaptureStr = state.prevCapture ? state.prevCapture[0] : '';
   const isStartOfLineCapture = listLookBehindRegex.exec(prevCaptureStr);
   if (!isStartOfLineCapture) {
     return null;
   }
   const fullSource = isStartOfLineCapture[1] + source;
   return listRegex.exec(fullSource);
 }
 
 // We've defined our own parse function for lists because simple-markdown
 // handles newlines differently. Outside of that our implementation is fairly
 // similar. For more details about list parsing works, take a look at the
 // comments in the simple-markdown package
 function parseList(
   capture: Capture,
   parse: Parser,
   state: State,
 ): UnTypedASTNode {
   const bullet = capture[2];
   const ordered = bullet.length > 1;
   const start = ordered ? Number(bullet) : undefined;
   const items = capture[0].match(listItemRegex);
 
   let itemContent = null;
   if (items) {
     itemContent = items.map((item: string) => {
       const prefixCapture = listItemPrefixRegex.exec(item);
       const space = prefixCapture ? prefixCapture[0].length : 0;
       const spaceRegex = new RegExp('^ {1,' + space + '}', 'gm');
       const content: string = item
         .replace(spaceRegex, '')
         .replace(listItemPrefixRegex, '');
       // We're handling this different than simple-markdown -
       // each item is a paragraph
       return parse(content, state);
     });
   }
 
   return {
     ordered: ordered,
     start: start,
     items: itemContent,
   };
 }
 
 function matchMentions(
   members: $ReadOnlyArray<RelativeMemberInfo>,
 ): MatchFunction {
   const memberSet = new Set(
     members
       .filter(({ role }) => role)
       .map(({ username }) => username?.toLowerCase())
       .filter(Boolean),
   );
   const match = (source: string, state: State) => {
     if (!state.inline) {
       return null;
     }
     const result = mentionRegex.exec(source);
     if (!result) {
       return null;
     }
     const username = result[2];
     invariant(username, 'mentionRegex should match two capture groups');
     if (!memberSet.has(username.toLowerCase())) {
       return null;
     }
     return result;
   };
   match.regex = mentionRegex;
   return match;
 }
 
 const blockQuoteRegex: RegExp = /^( *>[^\n]+(?:\n[^\n]+)*)(?:\n|$)/;
 const blockQuoteStripFollowingNewlineRegex: RegExp = /^( *>[^\n]+(?:\n[^\n]+)*)(?:\n|$){2}/;
 const maxNestedQuotations = 5;
 
 // Custom match and parse functions implementation for block quotes
 // to allow us to specify quotes parsing depth
 // to avoid too many recursive calls and e.g. app crash
 function matchBlockQuote(quoteRegex: RegExp): MatchFunction {
   return (source: string, state: State) => {
     if (
       state.inline ||
       (state?.quotationsDepth && state.quotationsDepth >= maxNestedQuotations)
     ) {
       return null;
     }
     return quoteRegex.exec(source);
   };
 }
 
 function parseBlockQuote(
   capture: Capture,
   parse: Parser,
   state: State,
 ): UnTypedASTNode {
   const content = capture[1].replace(/^ *> ?/gm, '');
   const currentQuotationsDepth = state?.quotationsDepth ?? 0;
   return {
     content: parse(content, {
       ...state,
       quotationsDepth: currentQuotationsDepth + 1,
     }),
   };
 }
 
+const spoilerRegex: RegExp = /^\|\|([^\n]+?)\|\|/g;
+
 export {
   paragraphRegex,
   paragraphStripTrailingNewlineRegex,
   urlRegex,
   blockQuoteRegex,
   blockQuoteStripFollowingNewlineRegex,
   headingRegex,
   headingStripFollowingNewlineRegex,
   codeBlockRegex,
   codeBlockStripTrailingNewlineRegex,
   fenceRegex,
   fenceStripTrailingNewlineRegex,
+  spoilerRegex,
   matchBlockQuote,
   parseBlockQuote,
   jsonMatch,
   jsonPrint,
   matchList,
   parseList,
   matchMentions,
 };