Some questions about correct PHP coding

I am somehow under the impression that ExtJs is built for web application not for simple websites.
For example, would you use ExtJs for a website like modx(the new version)

It’s a javascript library. You can use it for anything you want.

Here’s a basic accordion http://extjs.com/deploy/dev/examples/layout/accordion.html
Really nice tooltips http://extjs.com/deploy/dev/examples/simple-widgets/qtips.html

Here is some good advice on JS libraries: http://akshar.co.in/blog/archives/237