Umbraco 7 - XSLT Error Due to Missing Extension

I've been transferring a lot of our Umbraco 6.1.5 assets into a sandboxed copy of Umbraco 7. This is a fresh installation of Umbraco 7 but I have a page that makes use of the simple "lowercase" function using the syntax:

Exslt.ExsltStrings:lowercase(node)

The exact error I see occuring in the log is:

Cannot find a script or an extension object associated with namespace 'urn:Exslt.ExsltStrings

Has anything changed in the latest version of Umbraco? How can I run a lowercase function in 7? Is this build missing this extension object?

Thanks in advance for any assistance!


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/46995-umbraco-7-xslt-error-due-to-missing-extension