title: Is it possible to trigger a dash callback based on whether an Input field has been focused?
body: <p>As the title suggests I'd like to fire a dash callback upon focusing, i.e. clicking on a dcc.Input field.</p>
  <p>AFAIK one can only trigger one upon the Input field losing focus via the <code>n_blur</code> property. I already checked for the existence of a <code>n_clicked</code> property as the one that exists for buttons, which, however, didn't lead anywhere.</p>