Did you ever find yourself with unwanted whitespace at the start or end of your document? A tip to prevent this beforehand is to never close the PHP file with a _?> _tag. These tags are not required. It is a common practice on several projects.
If this is too late and you do have whitespace, execute the snippet below in the root folder to find the culprit.
<?php
foreach (glob('\*\*/\*.php') as $file){
if (preg_match('/\?'.'>\s\s+\Z/m',file_get_contents($file)))
echo $file . PHP_EOL; if( preg_match('/^[\s\t]+<?php/', file_get_contents($file)) )
echo $file . PHP_EOL;
}This code will match both the whitespace starting before the open and after the close tag.