Bug: Invalid group specifier on @lexical/markdown

[marcojacobsNL]

Lexical version:

Steps To Reproduce

• Use Safari v15, or iOS < 16.4
• Visit a site that uses Lexical with Markdown, e.g., https://playground.lexical.dev/
• Observe that the site fails to load due to an exception

SyntaxError: Invalid regular expression: invalid group specifier name

Link to code example:

lexical/packages/lexical-markdown/src/MarkdownImport.ts

Line 304 in 45e1df0

`(?<![\\\\\`])(\`)((?:\\\\\`|[^\`])+?)(\`)(?!\`)`,

In this file you can see the Regex that have the look behind expression that is causing the issue.

The current behavior

Lexical/the app crashes

The expected behavior

No crashes

Impact of fix

This breaks Lexical on affected browsers. caniuse indicates that Safari <16.4 (March 2023) is affected in particular.