[SimpleXML] echo the whole content of an element (without theelement)

I'm trying to understand Php Simple XML.
I have an xml file:

<resource>
<partners><acronym title="Free software foundation">Fsf</acronym> and
Isotype</partners>
</resource>

and I have loaded it into $resource

With Simple XML i would like to echo the ***whole content*** of the
element <partners>, i.e. "<acronym title="Free software
foundation">Fsf</acronym> and Isotype".

I have tried
1. $partners = $resource->partners->asXML()
echo $partners;
but it echoes "<partners><acronym title="Free software
foundation">Fsf</acronym> and Isotype</partners>". I don't want
<partners> and </partners>.
2. $partners = $resource->partners->children()->asXML()
echo $partners;
but it echoes only "<acronym title="Free software foundation">Fsf</
acronym>", without " and Isotype".

Thank you very much.