Prevent Quill from stripping attributes on block and inline elements

[lelamanolio]

I'm currently implementing Quill in a project that has both a WYSIWYG editor (converting from TinyMCE to Quill) and a code editor

If the user adds a class attribute on an <h1> tag and in another moment, try to change the same text from Quill, it automatically removes all attributes that were previously set.

After searching for similar issues, I found out a solution that works only partially:

const Inline = Quill.import("blots/inline");

const attributes = ["href", "class", "target"];

class KeepAttributes extends Inline {
  static create(value) {
    let node = super.create(value);
    if (value !== undefined) {
      if (value.href) node.setAttribute("href", value.href);
      if (value.target) node.setAttribute("target", value.target);
      if (value.class) node.setAttribute("class", value.class);
    }
    return node;
  }

  static formats(node) {
    return attributes.reduce((formats, attribute) => {
      if (node.hasAttribute(attribute)) {
        formats[attribute] = node.getAttribute(attribute);
      }
      return formats;
    }, {});
  }
}

It works partially because at the moment it works only for inline elements.
Even though I tried to have the same function extends both blocks and blocks/embed, Quill still strips all the attributes from the block elements.

Plus, an upgrade that it'd be neat would be to not have a "fixed" array of attributes, but rather that it automatically keeps all the attributes set on an element.

That's why I moved on from this solution and tried something else with the clipboard and its matchers.
I managed to create a function that appends the attributes of the element to its delta like so:

const keepAttributes = (node, delta) => {
  const attributes = [...node.attributes];
  const finalAttributes = {};

  attributes.forEach((attr) => {
    const attribute = attr.nodeName.replace(/-([a-z])/g, function (g) { return g[1].toUpperCase(); })
    const attributeValue = attr.nodeValue;
    finalAttributes[attribute] = attributeValue
  });

  delta.map((d) => {
    const currentAttributes = d.attributes;
    const newAttributes = { ...currentAttributes, ...finalAttributes };

    d.attributes = newAttributes
  })

  console.log(delta);

  return delta;
}

In the console.log() I can clearly see that the attributes were correctly added in the delta but still, when I invoke quill.clipboard.dangerouslyPasteHTML, it still strips all the attributes.
For more clarity, here's a simplified version of my code with the matcher mentioned: https://jsfiddle.net/b9d45zhk/17/

Anyone had the same kind of requirements/issues with it and can help?