Problem with whitespace before doctype

Question

I got some strange problem where i have 2 copies of same website in 2 different folders. In one of those 2 copies has whitespace before doctype declaration so i have problem

Answer 1

I just spent a day solving this problem where my libraries worked fine on static pages but under a dynamic system with a master script at the start (apache mod_write rewriting all to master script) the browser flipped into backward compat mode (js: alert(document.compatMode()) ) and distorted my styling. All my include files were ended properly and no echos, etc.. The problem? A blank line above the opening