JSFiddle - React, Tailwind, and code Playground

JavaScript

var xml = $.parseXML("<root/>"); // create XML document

var node = $("<foobar/>", document); // works
document.write("foobar (document): "+node.length+"<br />");

var node = $("<foo-bar/>", document); // works
document.write("foo-bar (document): "+node.length+"<br />");

var node = $("<foobar/>", xml); // works
document.write("foobar (xml): "+node.length+"<br />");

var node = $("<foo-bar/>", xml); // doesn't work
document.write("foo-bar (xml): "+node.length+"<br />");