code: function expandAnnotation (tx, anno, sel) {
    if (!sel || !sel._isSelection) throw new Error('Argument "selection" is required.')
    if (!anno || !anno.isAnnotation()) throw new Error('Argument "anno" is required and must be an annotation.')
    let annoSel = anno.getSelection()
    let newAnnoSel = annoSel.expand(sel)
    anno._updateRange(tx, newAnnoSel)
    return anno
  }
docs: /*
  @param {model/Document} tx
  @param {model/PropertyAnnotation} args.anno annotation which should be expanded
  @param {model/Selection}  args.selection selection to which to expand