Implementation of phpstorm View method

I would like to ask the gods, I in the phpstorm ctrl+ right click to enter a method, but this method is an empty method, where is his specific implementation? For example, the function str_replace:

Click on the method
clipboard.png
:

clipboard.png

but the method here is empty, so how does it implement the replacement function? Thank you!

Php
Mar.20,2021

  

github search php for source code

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