When the html document envelope is used, this function is used to get a html element where the return value is appended. It's the main function to override to provide custom HTML templates.

The default document provides a default stylesheet, our default javascript, and some timezone cookie handling (which you must handle on the server. Eventually I'll open source my date-time helpers that do this, but the basic idea is it sends an hour offset, and you can add that to any UTC time you have to get a local time).