Google star rating microformats

Yes, it's an old situation. In the google search results, one can display rating stars below the page title.
How to do it? What does one add to the HTML code so google displays those stars?
Something like the stars rating found in this image:
   

Here is the current version, in microformat (there are also other options). Note that this code is valid for the current time-being (e.g. 2015), this has been subject of change over the years.
So here's the snippet i'm using:

<div class="hreview-aggregate">
    <span class="item">
        <span class="fn">Restaurant Italia</span>
    </span>
    <span class="rating">
        <span class="average">4,5</span> din
        <span class="best">5</span>
    </span>
    Din <span class="votes">25</span> de voturi
</div>

The code is taken from https://support.google.com/webmasters/answer/146645?hl=en


Good luck!