
    This function is used to declare a new XPath extension function or
redefine an existing function.  It can be used in XPath queries and
XSLT stylesheets.  You should use QNames for extension functions.
Note that the standard XPath functions cannot be redefined.xpf_extension() stores the functions into
the SYS_XPF_EXTENSIONS system table.
    
    The input parameters will be retreived as a strings and then will be converted to the datatype of 
    the corresponding argument of the stored procedure. 
    