Get text positon for html element

Question

I am developing a plugin for obsidian inspired by the obsidian-todotxt-codeblocks plugin. For that I need to get the line where a codeblock is located. I tried to use 'editor.posAtDom(el)' for each codeblock, but get a RangeError. As this is working for teh obsidian-todotxt plugin, what am I missing?

My Code:

export default class MyPlugin extends Plugin {

    async onload() {
        await this.loadSettings();
        console.log("loaded settings");

        this.registerMarkdownCodeBlockProcessor("pergament", (source, el, ctx) => {
            console.log("registered markdown code processor");
            const text = document.createElement("div");
            text.innerHTML = source;
            text.id = "pergament";
            el.appendChild(text);
            
            console.log(el); 

            const markDownView: MarkdownView | null = this.app.workspace.getActiveViewOfType(MarkdownView)
            if (markDownView) {
                console.log("markdownView exists");
                const editorView: EditorView = markDownView.editor.cm as EditorView;
                console.log(editorView.scrollDOM);
                const pos = editorView.posAtDOM(el);
                const line = editorView.state.doc.lineAt(pos);
            }
        })
    }
}