First of all, you can't do <span itemprop="currency" content="RUB">руб.</span>
in microdata. The content
attribute is only valid on a meta element. So you could do <meta itemprop="currency" content="RUB">руб.
. Unlike normal <meta>
elements, these can appear in the <body>
section of the page. However, there's no direct microformat equivalent of this.
But you could also do <data itemprop="currency" value="RUB">руб.</data>
to achieve the same thing in microdata, and it seems that the similar <data class="currency" value="RUB">руб.</data>
will do the same job in microformats - see http://microformats.org/#time-data - at least in principle, since it's still quite new.
Failing that, I believe that the old way of doing this in microformats was <abbr class="currency" title="RUB">руб.</abbr>
but this is horrible semantics and I would heavily discourage it.