Each PHP variable exists in a variable container called "Zval". A Zval variable container that includes two bytes of extra information in addition to the type and value of the variable. The first is "Is_ref", which is a bool value that identifies whether the variable belongs to a reference collection (reference set). With this byte, the PHP engine can differentiate between normal and reference variables, and since PHP allows users to use the custom reference by using &, there is an internal reference counting mechanism in the Zval variable container to optimize memory usage. The second extra byte is "RefCount", which represents the number of variables (also known as symbols) that point to the Zval variable container. All symbols exist in a symbol table, where each symbol has scope (scope), and those main scripts (for example, scripts that are requested by the browser) and each function or method also have scopes.
When a variable is assigned a constant value, a Zval variable container is generated, as in the following example:
Example #1 Create a new Zval container
<?php $a = "new string"; ? >
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