Here's a pattern I use for this type of situation. In your main template, set up some variables:
//layouts/default.jade
- var bodyClass;
block variables
html
head
body(class=bodyClass)
section.main-content
block content
Then establish the bodyClass
in your page templates.
//about.jade
extends ../layouts/default
block variables
- bodyClass = "about"
block content
h1 This is the About Page
This is how I do my page titles for the <head><title>
tag, for example. I can also have logic in the layout.jade
file to provide default values, etc.