Function document 

pub fn document(title: &str, head: Vec<El>, body: El) -> String

A whole page: the doctype, the head this Cockpit always emits, and a body.

The head is not a template a page may replace. Its content — the character set, the viewport, the stylesheet, the theme script that runs before first paint — is the same on every page by construction, so a new page cannot forget the parts that make the Cockpit behave.