instance of that class.
a - array (zval*)
+ A - array or object (zval *)
b - boolean (zend_bool)
C - class (zend_class_entry*)
d - double (double)
f - function or array containing php method call info (returned as
zend_fcall_info and zend_fcall_info_cache)
h - array (returned as HashTable*)
+ H - array or HASH_OF(object) (returned as HashTable*)
l - long (long)
o - object of any type (zval*)
O - object of specific type given by class entry (zval*, zend_class_entry)