internals
What a PHP variable actually is
A zval is sixteen bytes, a value union and a type tag. What that tag says decides whether an assignment copies anything, what a reference costs, and which variable pays.
Internals
The engine: compilation, the Zend VM, memory layout, and the data structures behind the values you pass around.
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internals
PHP arrays are not arrays
One structure serves as list, dictionary and set. Packed and hashed layouts, what each costs in memory, and when a conversion happens.
internals
What happens when PHP runs your code
A request walks from the SAPI to the Zend VM — lexing, compilation to opcodes, the OPcache lookup that skips both, and execution.