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.

How is it clear?  Because you've indented it that way? :)

It's not clear at all, and in fact, the solution for the dangling else  
 
shift/reduce problem clearly states that the else belongs to the closest
 
IF.   
   
PHP makes no distinction between if's with braces, no braces, or colons,
 
and it doesn't pay attention to your indentation either.  As soon as it 
 
sees the elseif, it expects it to match the inner IF sentence, and since
 
it doesn't, it fails.