The first sentence reads: "'Include what you use' means this: for every symbol (type, function variable, or macro) that you use in foo.cc, either foo.cc or foo.

The first sentence reads: "'Include what you use' means this: for every symbol (type, function variable, or macro) that you use in foo.cc, either foo.cc or foo.h should #include a .h file that exports the declaration of that symbol." For clarity and correctness, I think it should be changed to: "'Include what you use' means this: for every symbol (type, function variable, or macro) that you use in foo.cc that is not declared in foo.cc, either foo.cc or foo.h should #include a .h file that exports the declaration of that symbol." Not having that phrase tripped me up for a few minutes. I guess everyone else thinks it's implied, but for some reason that wasn't clear to me until I read through more of their documentation.