anchor.diff:  define additional viewports by giving the CSS property `{ overflow-y: scroll }` to any `<div>`.
   
   
  -Revealing new content
  ----------------------
  +\#\#\# Revealing new content
   
   When following a [link to a fragment](/a-up-target) Unpoly will automatically
   scroll the document's viewport to [reveal](/up.viewport) the updated content.
  
positive.code: you should so Unpoly can pick the right viewport to scroll for each fragment update.
  
  
  Bootstrap integration
  ---------------------
  
  When using Bootstrap integration (`unpoly-bootstrap3.js` and `unpoly-bootstrap3.css`)
  Unpoly will automatically be aware of sticky Bootstrap components such as
  
negative.code: 
    If no element matches the given `#hash` anchor, a resolved promise is returned.
  
    \#\#\# Example
  
        up.revealHash('#chapter2')
  
    @function up.viewport.revealHash
    @param {string} hash
  
    @return {Promise}
      A promise that is fulfilled when scroll position has changed to match the location hash.
    @experimental
  