When interpolating PHP's string-indexed array elements (5.3.3, Win32) the following behavior may be expected or not:
$ha = array('key1' => 'Hello to me');
print $ha['key1']; # correct (usual way)
print $ha[key1]; # Warning, works (use of undefined constant)
print "He said {$ha['key1']}"; # correct (usual way)
print "He said {$ha[key1]}"; # Warning, works (use of undefined constant)
print "He said $ha['key1']"; # Error, unexpected T_ENCAPSED_AND_WHITESPACE
print "He said $ha[ key1 ]"; # Error, unexpected T_ENCAPSED_AND_WHITESPACE
print "He said $ha[key1]"; # !! correct (How Comes?)
Inerestingly, the last line seems to be correct PHP code. Any explanations? Can this feature be trusted?
Edit: The point of the posting now set in bold face in order to reduce misunderstandings.