Basic PHP implementations, opcodes, and internal work

The main purpose of this paper is to investigate how PHP works internally and how variables, arrays, objects, and other types are stored in memory. The paper will cover generated series of operation codes, commonly known as "opcodes", and why advanced PHP programmers should know the basics of PHP "under-the-hood". Additionally, it aims to show how function calls and classes work internally, basic concepts such as "pre-increment or post-increment speed comparison", and minor optimization recommendations.