Setting XPath Variables
An XPath expression supplied to the JAXP XPath API can contain undeclared variables, for
example a valid expression might be
//emp[@ssn=$SSN]. The value of the variable
$SSN must be supplied by the calling application when the expression is evaluated.
The mechanism for doing this is the
VariableResolver: when Saxon encounters an
undeclared variable like
$SSN, it calls the user-supplied
which is expected to return the corresponding value.
The Java value returned by the
VariableResolver is converted to an XDM
value using the rules described at Converting Java values to XDM values.