Don't unwrap mrow when created fenced elements (in case attributes have been attached to the mrow). Resolves issue mathjax#1415.

Author: dpvc

unpacked/jax/input/TeX/jax.js

@@ -2210,9 +2210,11 @@
      */
     fenced: function (open,mml,close) {
       var mrow = MML.mrow().With({open:open, close:close, texClass:MML.TEXCLASS.INNER});
-      mrow.Append(MML.mo(open).With({fence:true, stretchy:true, texClass:MML.TEXCLASS.OPEN}));
-      if (mml.type === "mrow") {mrow.Append.apply(mrow,mml.data)} else {mrow.Append(mml)}
-      mrow.Append(MML.mo(close).With({fence:true, stretchy:true, texClass:MML.TEXCLASS.CLOSE}));
+      mrow.Append(
+        MML.mo(open).With({fence:true, stretchy:true, texClass:MML.TEXCLASS.OPEN}),
+        mml,
+        MML.mo(close).With({fence:true, stretchy:true, texClass:MML.TEXCLASS.CLOSE})
+      );
       return mrow;
     },
     /*