Help with Implementation of Equation Block

[tohhongxiang]

Hi everyone, I'm currently trying to implement a markdown shortcut for an equation block, which transforms the following into an equation block (non-inline katex)

$$
\sqrt{2}
$$

I wanted the transformer to be able to meet the following requirements:

1. When a user types $$ followed by a newline, their equation, another newline, and then closing with $$, it will automatically convert to an equation block
2. When a user pastes such a block of text into the editor, it is rendered properly as an equation block, with the corresponding equation inside

I'm currently using an ElementTransformer to parse the text, and then convert the text into an equation block node. My current code looks something like this:

export const EQUATION_BLOCK: ElementTransformer = {
    dependencies: [EquationNode],
    export: (node: LexicalNode) => {
      if (!$isEquationNode(node)) {
        return null;
      }
      const equation = node.getEquation();
      return (
        '$$' +
        (equation ? '\n' + equation : '') +
        '\n' +
        '$$'
      );
    },
    regExp: /^\$\$(\r\n|\r|\n)+([^$].+?)(\r\n|\r|\n)+\$\$/,
    replace: (parentNode, children, match) => {
        console.log("Matched equation block", parentNode, children, match)
        const equationNode = $createEquationNode("equation", false);
        equationNode.append(...children)
        parentNode.replace(equationNode);
        equationNode.select(0, 0)
    },
    type: 'element',
  };

I am then using this transformer and pass it into the MarkdownShortcuts plugin: (not the default one provided by @lexical/markdown

<MarkdownShortcutPlugin transformers={TRANSFORMERS} />

I also have a paste event handler:

export default function MarkdownCopyPastePlugin() {
    const [editor] = useLexicalComposerContext()

    useEffect(() => {
        editor.registerCommand<ClipboardEvent>(
            PASTE_COMMAND,
            (event) => {
                const pastedText = event.clipboardData?.getData('Text')
                
                if (pastedText) {
                    editor.update(() => {
                        $convertFromMarkdownString(pastedText, TRANSFORMERS)
                    })
                }

                return true
            },
            COMMAND_PRIORITY_EDITOR
        )
    }, [editor])

    return null
}

This code was referenced from the CODE transformer and the EQUATION transformer

However, replace is not firing, and I'm not sure why. Does regExp only support single-line matches? What should I do to allow replace to trigger properly? Any pointers to the right direction is appreciated. Thanks for the great library!