As a derivation of this, in general I advise reading framework source code. Not because you should write code like that, but to learn what the language can do. Framework source code has often been refined by several people over a longer period of time, honed to avoid rough edges. I think you can learn a lot about designing an API, writing good abstractions, and encapsulating complexity.
I would caution this. Not because it's a bad idea, but because I've experienced juniors reading framework often ended up creating over-engineered codes that lean heavily into meta style programming. Their code become overly-complex due to massive amount of abstractions they put in. I like the old saying, "cook the recipe exactly as it is three times before you can add your own spin to it".