context.popDocumentContext();
        protected Sequence execute() throws XPathException {            context.functionStart(functionDef.getSignature());            LocalVariable mark = context.markLocalVariables(true);            try {                Sequence returnSeq = expression.eval(contextSequence, contextItem);//                LOG.debug("Returning from execute()");                return returnSeq;            } catch(XPathException e) {                if(e.getLine() == 0)                    e.setASTNode(getASTNode());                // append location of the function call to the exception message:                e.addFunctionCall(functionDef, getASTNode());                throw e;            } finally {                context.popLocalVariables(mark);                context.functionEnd();            }        }