fix: reject self-closing tags as multiple root nodes in validator

spec/validator_spec.js

@@ -403,6 +403,30 @@ describe("should not validate XML documents with multiple root nodes", () => {
             InvalidXml: 'Multiple possible root nodes found.'
         }, 5);
     });
+
+    it('when a self closing root node is followed by another self closing node', () => {
+        validate(`<xml/><xml2/>`, {
+            InvalidXml: 'Multiple possible root nodes found.'
+        });
+    });
+
+    it('when a self closing root node is followed by a paired node', () => {
+        validate(`<xml/><xml2></xml2>`, {
+            InvalidXml: 'Multiple possible root nodes found.'
+        });
+    });
+
+    it('when a paired root node is followed by a self closing node', () => {
+        validate(`<xml></xml><xml2/>`, {
+            InvalidXml: 'Multiple possible root nodes found.'
+        });
+    });
+
+    it('when a self closing root node is followed by trailing text', () => {
+        validate(`<xml/>extra`, {
+            InvalidXml: 'Extra text at the end'
+        });
+    });
 });
 
 describe("should report correct line numbers for unclosed tags", () => {

src/validator.js

@@ -91,6 +91,14 @@ export function validate(xmlData, options) {
           const isValid = validateAttributeString(attrStr, options);
           if (isValid === true) {
             tagFound = true;
+            //a self closing tag at the root level is a complete root element
+            if (tags.length === 0) {
+              //if the root level has already been reached, this is a second root
+              if (reachedRoot === true) {
+                return getErrorObject('InvalidXml', 'Multiple possible root nodes found.', getLineNumberForPosition(xmlData, tagStartPos));
+              }
+              reachedRoot = true;
+            }
             //continue; //text may presents after self closing tag
           } else {
             //the result from the nested function returns the position of the error within the attribute