XSLT Reference : Using Extension Objects : Microsoft Extensions
 
Microsoft Extensions
Extension objects that are defined and implemented by Microsoft as part of the .NET XSL transform runtime.
Purpose
Microsoft implemented additional methods not part of the XSLT 1.1 standard. This work was done prior to the XSLT 2.0 and EXSLT specifications being finalized.
Namespace
urn:schemas-microsoft-com:xslt
Prefix
msxsl
Method
msxsl:node-set(string textualXML):
Description
Converts textual XML into a node set in a new XML document. Most often used to convert intermediate XML back into a working node set for additional processing.
Returns
A node set equivalent to the provided textual XML.
Note: The Microsoft XSL transform engine also supports custom extensions defined with script blocks.