WordPress: Restrict MathJax to a class

I write on a variety of topics, only some of which it's appropriate to have mathematical typesetting for. To avoid triggering a math rendering engine on unrelated use of $purious dollar sign$, while activating it when $\text{necessary}\wedge\text{appropriate}$, I decided to restrict them to only <… lang="x-mathjax">. Here's how that's done (for v3):

MathJax = {
	tex: {
		inlineMath: [
			['$', '$']
		]
	},
	startup: {
		elements: [':lang("x-mathjax")']
	}
};

I also recommend adding the following CSS to the admin-area with a userstyle or something:

.mce-content-body :lang("x-mathjax") {
	background-color: peachpuff;
}