how many (generic ?) class wordpress have?

what i meant with generic is those class that create by non lead wordpress programmer. i just start reading开发者_StackOverflow社区 the source code directly and encounter a class who name filereader and i use it to read stream of file.

Is there any other useful class ? i would like to know so i can utilize it when work on wp ?

I know this is a question spesific for wordpress developer. But i would like the hear any suggestion. anything. Even its a mislead question. ;D

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