@atlaskit/adf-schema/dist/es2019/schema/marks/unsupported-mark.js

Shared package that contains the ADF-schema (json) and ProseMirror node/mark specs

import { unsupportedMark as unsupportedMarkFactory } from '../../next-schema/generated/markTypes';
export const unsupportedMark = unsupportedMarkFactory({
  toDOM() {
    return ['span'];
  }
});