title: How "aria-describedby" and "aria-hidden" attributes work in bootstrap?
body: <p>I have found these attributes in many places of bootstrap.I searched about them in google and ask many people about them.But can not find proper answer.</p>
  
  <p>Though i found some answer about "aria-hidden" in this site,still it is not clear to me properly.So,it will be helpful if someone describe me about "aria-hidden" and "aria-discribedby".</p>