Out-of-the-box, the Search Core Results web part only supports XSLT 1.0. The last thing I read from Chris Lovett on the MS XML team is that Microsoft don't have plans for XSLT 2.0. This makes the possibilities limiting at times!
Is there any way to use a custom library such as EXSLT within this web part to enhance transforms with regular expressions and other functionality?
I have previously had to inline the custom libraries functions into an xslt file hosted in SharePoint and linked to the xslt property in the webpart (I prefer linking to a file over adding the xslt in directly).
Linking libraries seems to produce a security issue and you are certainly not allowed to reference C# functions in the xslt.
In cases where I have more advanced functions required from any xslt rendering, I have resorted to creating a custom webpart.
The problem here is on the browser side, since XSLT 2.0 is not supported in IE8.
I wish I could provide you with a better answer here but I tried to implement EXSLT within data view web part, and failed! I am not an XSLT guru, but I think the problem was caused with some incompatibilities with the dwp namespace. At the end I gave up :(.
