code: function sortMarksByOccurences(span, i, spans) {
    if (!span.marks || span.marks.length === 0) {
      return span.marks || []
    }
  
    const markOccurences = span.marks.reduce((occurences, mark) => {
      occurences[mark] = occurences[mark] ? occurences[mark] + 1 : 1
  
      for (let siblingIndex = i + 1; siblingIndex < spans.length; siblingIndex++) {
        const sibling = spans[siblingIndex]
  
        if (sibling.marks && Array.isArray(sibling.marks) && sibling.marks.indexOf(mark) !== -1) {
          occurences[mark]++
        } else {
          break
        }
      }
  
      return occurences
    }, {})
  
    const sortByOccurence = sortMarks.bind(null, markOccurences)
  
    // Slicing because sort() mutates the input
    return span.marks.slice().sort(sortByOccurence)
  }
docs: We want to sort all the marks of all the spans in the following order: 1. Marks that are shared amongst the most adjacent siblings 2. Non-default marks (links, custom metadata) 3. Built-in, plain marks (bold, emphasis, code etc)