How do you extract text matching a pattern in XPATH?

I have data that looks like this:

<value>v13772   @FBst0451145:w&lt;up&gt;1118&lt;/up&gt;; P{GD3649}v13772@
v13773  @FBst0451146:w&lt;up&gt;1118&lt;/up&gt;; P{GD3649}v13773@</value>

How can I process this string in XPATH to extract any and all @FBst####### numbers?

I know of the xpath matches() function... but that only returns true or false. No good if I want the matching string. I've searched around but cannot find a satisfactory answer to this problem, which is probably really common.

Thanks!