| SAXONICA | 
A Saxon extension instruction is invoked using a name such as <saxon:localname>.
         
The saxon prefix (or whatever prefix you choose to use) must be associated with the
            Saxon namespace URI http://saxon.sf.net/. The prefix must also be designated as an
            extension element prefix by including it in the
            extension-element-prefixes attribute on the xsl:stylesheet element, or the
            xsl:extension-element-prefixes attribute on any enclosing literal result element or
            extension element.
         
However, top-level elements such as saxon:collation and
            saxon:script can be used without
            designating the prefix as an extension element prefix.
         
The extension instructions and declarations are:
saxon:assign: assigns a new value to a global variable
saxon:call-template: calls a template whose name is decided at run-time
saxon:collation: names and describes a collating sequence
saxon:doctype: constructs a serialized DOCTYPE declaration
saxon:import-query: imports functions from an XQuery library module
saxon:entity-ref: creates an entity reference in the serialized output
saxon:script: declares an extension function
saxon:while: iterates until a condition becomes false