Add custom attribute

[MisterBalboa]

Hi there,

I need to add a dynamic class to each

tag every time I call setContents.

something like

window.quill.setContents([
    { insert: "hello", attributes: { customKey: condition ? 'class-a' : 'class-b' } }
]);

I am able to hack my way in the Block class

class Block extends BlockBlot {
  ...
  formatAt(index, length, name, value) {
    if (length <= 0) return;
    if (name === 'customKey') this.domNode.classList.add(value);
    ...
  }

but the attribute is not stored in quill inner structure, quill.getContents does not store my attributes.customKey, I tried adding it to /formats folder without success.

Is there any official way to do this?
any suggestions?