Explain how the Zend Engine works internally in PHP.

The Zend Engine is the core runtime engine of PHP responsible for parsing, compiling, optimizing, and executing PHP code.

The Zend Engine is the heart of PHP. It acts similarly to a virtual machine and execution runtime. Understanding the Zend Engine is extremely valuable for senior engineers working on performance-sensitive applications, extensions, profiling tools, or debugging production bottlenecks.

Execution lifecycle:

The lexer tokenizes PHP source code into meaningful tokens. Example:

The parser converts tokens into an Abstract Syntax Tree (AST). This stage validates syntax correctness.

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