Accessing context from xsl:function body

Hi all,
  Could somebody please answer this for me ...

Recently I was solving some problem, where I needed the capability for
the xsl:function body to be able to access the context (the
environment from where the function was called, say a particular XPath
expression).

But the XSLT 2.0 spec states ...
"Within the body of a stylesheet function, the focus is initially
undefined; this means that any attempt to reference the context item,
context position, or context size is a non-recoverable dynamic error.
[XPDY0002]"

Why does XSLT 2.0 language prohibits xsl:function to access the
context information?

On the contrary, the named template can access the context
information. Why is this difference in capability on named template,
and xsl:function?

Is there any use case, where xsl:function body would really need the
context information? Is there a merit in the argument, to provide this
capability to xsl:function?

-- 
Regards,
Mukul Gandhi