fix: validator; reject an XML declaration inside an element

spec/validator_spec.js

@@ -267,6 +267,15 @@ describe("XML Validator", function () {
         });
     });
 
+    it("should not validate XML declaration inside an element", function () {
+        validate("<foo><?xml version=\"1.0\"?></foo>", {
+            InvalidXml: "XML declaration allowed only at the start of the document."
+        });
+        validate("<foo>bar<?xml?></foo>", {
+            InvalidXml: "XML declaration allowed only at the start of the document."
+        });
+    });
+
     it("should not validate XML with prolog only", function () {
         validate("<?xml version=\"1.0\" standalone=\"yes\" ?><!--some comment -  end in this line-->", {
             InvalidXml: "Start tag expected."

src/validator.js

@@ -149,7 +149,7 @@ export function validate(xmlData, options) {
               i = readCommentAndCDATA(xmlData, i);
               continue;
             } else if (xmlData[i + 1] === '?') {
-              i = readPI(xmlData, ++i);
+              i = readPI(xmlData, i + 2);
               if (i.err) return i;
             } else {
               break;