canCreate (annos, sel, context) {
    // to create an annotation we need an expanded selection
    if (sel.isCollapsed()) return false
    // fine if there is no other anno of this type yet
    if (annos.length === 0) return true
    // otherwise these annos are only allowed to 'touch' the current selection, not overlap.
    for (const anno of annos) {
      if (sel.overlaps(anno.getSelection(), 'strict')) return false
    }
    return true
  }
Checks if new annotations could be created.
    There should be no annotation overlapping, selection must be not collapsed.

    @param {array} annos annotations
    @param {Selection} sel selection
    @param {object} context

    @returns {Boolean} Whether or not annotation could be created.