title: When to use prop modifier in vue?
body: <p>When to use prop modifier in vue?</p>
  <p>In vue document,I find the prop modifier in v-bind here: <a href="https://v2.vuejs.org/v2/api/#v-bind" rel="nofollow noreferrer">https://v2.vuejs.org/v2/api/#v-bind</a></p>
  <p>my question is this:
  <a href="https://i.stack.imgur.com/xJg1a.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xJg1a.png" alt="enter image description here" /></a></p>