Remove "u" flag intentionally (#4191)

* Remove "u" flag intentionally

* Add entry

CHANGELOG.md

@@ -60,6 +60,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
    -  Fixed overlapping hit zone causing clicking on bottom edge of message bubble may focus on the next activity instead
    -  Fixed typings of `useFocus` and `useLocalizer`
 -  Fixes [#3165](https://github.com/microsoft/BotFramework-WebChat/issues/3165) and [#4094](https://github.com/microsoft/BotFramework-WebChat/issues/4094). Allowlist `aria-label` for links in Markdown and skip unrecognized attributes or invalid curly brackets, by [@compulim](https://github.com/compulim), in PR [#4095](https://github.com/microsoft/BotFramework-WebChat/pull/4095)
+-  Fixes [#4190](https://github.com/microsoft/BotFramework-WebChat/issues/4190). Recent Markdown curly bracket fix should not break IE11 due to unsupported "u" flag in `RegExp`, by [@compulim](https://github.com/compulim), in PR [#4191](https://github.com/microsoft/BotFramework-WebChat/pull/4191)
 
 ### Changed
 

packages/bundle/src/renderMarkdown.ts

@@ -59,13 +59,15 @@ const internalMarkdownIt = new MarkdownIt();
 
 const MARKDOWN_ATTRS_LEFT_DELIMITER = '⟬';
 // Make sure the delimiter is free from any RegExp characters, such as *, ?, etc.
-// eslint-disable-next-line security/detect-non-literal-regexp
-const MARKDOWN_ATTRS_LEFT_DELIMITER_PATTERN = new RegExp(MARKDOWN_ATTRS_LEFT_DELIMITER, 'gu');
+// IE11 does not support "u" flag and Babel could not remove it. We intentionally omitting the "u" flag here.
+// eslint-disable-next-line security/detect-non-literal-regexp, require-unicode-regexp
+const MARKDOWN_ATTRS_LEFT_DELIMITER_PATTERN = new RegExp(MARKDOWN_ATTRS_LEFT_DELIMITER, 'g');
 
 const MARKDOWN_ATTRS_RIGHT_DELIMITER = '⟭';
 // Make sure the delimiter is free from any RegExp characters, such as *, ?, etc.
-// eslint-disable-next-line security/detect-non-literal-regexp
-const MARKDOWN_ATTRS_RIGHT_DELIMITER_PATTERN = new RegExp(MARKDOWN_ATTRS_RIGHT_DELIMITER, 'gu');
+// IE11 does not support "u" flag and Babel could not remove it. We intentionally omitting the "u" flag here.
+// eslint-disable-next-line security/detect-non-literal-regexp, require-unicode-regexp
+const MARKDOWN_ATTRS_RIGHT_DELIMITER_PATTERN = new RegExp(MARKDOWN_ATTRS_RIGHT_DELIMITER, 'g');
 
 export default function render(
   markdown: string,