I'm under the impression that if you are already a sort-of-proficient programmer in a dynamic scripting language such as Python or PHP, you should study the cod

I'm under the impression that if you are already a sort-of-proficient programmer in a dynamic scripting language such as Python or PHP, you should study the code of the VM where said language runs. I learnt a lot reading CPython's code after learning Python, even not being an expert on VMs nor on C++. I also had to work with PHP's VM for a research project and learnt a lot from tinkering with it. In both cases the code is not a piece of art, but you get practical knowledge about, for example, the misses and pitfalls of the languages you are already proficient with.