How many id's can contain the itemref?

If you look onto this working example of itemref usage:

<table>
 <col itemscope itemref="a0 a1 a2"></col>
 <tr>
  <th>Who</th>
   <td id=a0 itemprop=band>Tub Ring</td>
 </tr>
 <tr>
  <th>When</th>
   <td id=a1><time itemprop=date datetime=2010-01-01>The Big Fool Day!</time></td>
 </tr>
 <tr>
  <th>Where</th>
   <td id=a2 itemprop=location>Atlantis!</td>
 </tr>
</table>

, you see, that itemref can contain some id's, just divided by a space. My question is: how many? How many id's i can put into itemref?

I have a page with 4 types and ca. 80 properties.

The easiest way is not to brake the brain about nesting of them all, but write all properties just one aftter one down giving them an id, and then take a type and put all the id's, which must belong to it into its itemref.
The "right" way is to make the nesting, where it is possible, on other places use itemref.

Would somebody give me an advice?

thanks

Solution

Put as many as you like. The standard sets no restriction and any implementation specific limit of the number of properties is most unlikely to be lower for itemrefs than for properties established via descendent elements.