oop - How can I find the file path of any function or what it contains in PHP?

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When I do frontend development with PHP, I encounter statements similar to the following.

For example;

$this->getTheme()->getConfig('text_top', true);

For example, I want to find in which folder the "getConfig()" function is defined? Because I'm curious about the content? ie how the funtion is defined, what parameters it takes.

Is there a way to find this in php? Or it would be useful to see how the function is defined instead of the file path.

Thanks in advance for your answers.