What is the meaning of this tag: <t>lorem ipsum</t>

Question

The template page http://www.blacktie.co/demo/kelvin contains a tag I haven't seen before: <t>Email</t>

The corresponding CSS styles this: #footwrap t {font-weight: 700;}

I'm curious as to the significance of the <t>. It's not listed at http://htmldog.com/reference/htmltags or other lists I can find.

Is this a custom HTML tag? From what I've read about custom elements (eg http://www.html5rocks.com/en/tutorials/webcomponents/customelements) you need to call document.registerElement() or document.createElement() but this doesn't seem to be the case here.

Is this code semantically correct, or should it be written as:

<span class="t">Email</span>

#footwrap .t {font-weight: 700;}

Solution

Yes, the <t> tag is a custom element. While custom tags can be useful, if you want them supported in all browsers, you have to register the element with JS:

var tTag = document.registerElement('t');

More about custom tags here
So to answer your question, the coding is not valid, unless they have registered the element with the browser with JavaScript.
Sometimes, its just easier to use a class :D