$re = '/(?m)^Foo\K(?:(?!^Foo)[\S\s])+(?=^Yes)/';
$str = 'Foo $var1 <br/>
......... <br/>
......... <br/><br/>
Foo $var2 <br/>
..........<br/>
..........<br/>
..........<br/>
Yes
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php