Prevent text in ProseMirror-Document from automatically moving up when previous node is emptied

I have the following custom schema (shortened to only relevant parts):

const schema = new Schema({
  nodes: {
    doc: {content: 'title section+'},
    title: {
      content: 'text*',
      marks: "",
      isolating: true,
      toDOM() { return ["span", {class: "document-title"}, 0] },
      parseDOM: [{tag: "span.document-title"}]
    },
    section: {
      group: 'section',
      content: 'block+',
      toDOM() {return ['section', 0]}
    },
    paragraph: {
      content: "inline*",
      group: "block",
      parseDOM: [{ tag: "p" }],
      toDOM() { return ['p', 0]; }
    },
    text: {
      group: 'inline',
      inline: true
    }
  }
})

My Document looks something like this:

My document title <– withing span.document-title
My document body <– within section

in HTML it would – according to my schema – look like this:

<span class="document-title">My document title</span>
<section>My document body</section>

Here’s my problem:
When I delete everything in the title, the content of the <section> moves up, so now my title would be "My document body".
This is not what I want to happen.
I want the document body (everything within the <section>) to stay where it is and the title should be treated sort of like another editor, so nothing I do inside the title affects the body.

I thought setting "isolating: true" on the title would achieve exactly this behavior since the official documentation states:

When enabled, the sides of nodes of this type count as boundaries that regular editing operations, like backspacing or lifting, won’t cross.

However, it does not seem to do anything.

>Solution :

I would separate the node type for the title that way you keep it outside of the main document structure like this:

nodes: {
    doc: { content: "section+" },
    title: {
      content: "text*",
      group: "title",
      toDOM() {
        return ["h1", { class: "document-title" }, 0];
      },
      parseDOM: [{ tag: "h1.document-title" }],
    },
    section: {
      content: "block+",
      toDOM() {
        return ["section", 0];
      },
    },

That should prevent unwanted movement because it would now be part of a separate node.