======XPath Extensions======

With Version 0.1.0.0 an XPath extension is available in xmlsh which allows calling into xmlsh from with any xpath context including xpath, xlst, xquery, and the builtin <[ ... ]> commands.



The namespace "xmlsh" is **predeclared** for the XML expression syntax  <[ ... ]> as well as the [[CommandXQuery xquery]], [[CommandXPath xpath]] and  [[CommandXslt xslt]] commands.

For example, the following works without using an explicit declaration
%%
echo <[  <foo/>/xmlsh:eval("xcat") ]>
%%

Similary the syntax to xquery is supported
%%
xquery -n -q 'xmls:eval("echo hi")'
%%



====Extension functions implemented====

===eval===

The **eval** xpath function evaluates its first argument as an xmlsh string (identical to the [[CommandEval eval]] command) and optionally its second argument as positional parameters.   The return value of the eval function is the standard output of the command.

Examples
%%
xecho <[ xmlsh:eval("xecho $*" , ("foo" , <bar/> , 1 )  )  ]>
xquery -n 'xmlsh:eval("xls")'
xpath -n 'xmlsh:eval("xls $*" , "*.xml")'
var=<[ xmlsh:eval("xls") ]>
%%

===Calling XSLT from XQuery.   ===

An interesting use of eval is to call xslt from within xquery or visa-versa.    The context is passed to eval as the stdin and the output of the command becomes the result value of the expression.  These examples are in xquery either via the <[ ]> syntax or the [[CommandXquery xquery]] command and require calling xquery from xmlsh to activate the extension function.

Example, in an XQuery expression, or file run from xmlsh
%%
/foo/bar/xmlsh:eval("xslt -f style.xsl")/spam
%%
calls "xslt" with the sytlesheet  "style.xsl" passing the input context from /foo/bar as the input and then the output is further evaluated to extract the /spam child

An alternative of the above which can use variables for the stylesheet 
%%
let $style := "style.xsl"
return 
/foo/bar/xmlsh:eval("xslt" , ("-f" , $style) )/spam
%%

An alternative which passes the input context as a third argument 
%%
let $style := "style.xsl"
return 
xmlsh:eval("xslt" , ("-f" , $style), /foo/bar  )/spam
%%