Variables are set before or by other requiring file.
if (!$a and isset($b, $c) and # line 1
($d OR isset($e) && $f) ) # line2 # The parentheses are not necessary and can be safely removed.PHP(PHP7102) / Hint: Remove unnecessary parenthesesPHP(PHP7103)
if (line1 and line2)
but
if (!$a and isset($b, $c) and $d # line1
OR isset($e) && $f ) # line2
means if ( line1 OR line2 )