When does reflow happen in a DOM environment?

Question

What kinds of activities will trigger reflow of web page with DOM?

It seems there are different points of view. According to http://www.nczonline.net/blog/2009/02/03

Answer 1

document.body.style.display = 'none';
document.body.style.display = 'block';

This often solves those incomprehensible layout bugs.