validate send *expr attributes at parse time

[mattoshry]

https://www.w3.org/TR/scxml/#send
The following should be ECMA-validated at parse time: 'delayexpr', 'eventexpr', 'targetexpr', 'typeexpr'

If they are not valid ECMAScript expressions, the document should be rejected.

Unclear what validation the code at [1] is performing. Won't node will always have a $type ('send')? Is 'expr' a valid attribute of send?

			'send': function (node) {
				if(node.$type) {
					return validateJavascriptExpression(node.expr);
				}

				return [];

[1]

SCION/lib/compiler/static-analysis/scjson-analyzer.js

Line 153 in cbdf5dd

if(node.$type) {