This script causes a parser error:
<?
$a = $b = 2;
if ($a==2):
	if ($b==2) print "a=2 b=2<br>";
elseif ($a=3):
	print "a=3<br>"
endif;
?>
This script also fails:
<?
$a = $b = 2;
if ($a==2):
	if ($b==2) {print "a=2 b=2<br>"};
elseif ($a=3):
	print "a=3<br>"
endif;
?>

Based in the fact that this code isn't correct:

if ($b==2) print "a=2 b=2<br>";
elseif ($a=3): 
     print "a=3<br>";
endif;

i think it's clear the elseif ($a=3):
belongs to the previous if sentence.