Writing custom selectors is highly experimental!

"el" is the full DOM of the page. So you can write things like:

• el.querySelector(".posttitle").innerHTML
• el.querySelector("div").innerText
• el.querySelector("*[itemprop='author']").innerText

The code uses eval() under the hood(!) so be warned...

Here's an example:
domain: tomcritchlow.com
title: post-title
selector: el.querySelector(".posttitle").innerHTML

More custom selectors here: See here for a guide