The first sentence reads: &quot;&#x27;Include what you use&#x27; 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.&quot;<p>For clarity and correctness, I think it should be changed to: &quot;&#x27;Include what you use&#x27; means this: for every symbol (type, function variable, or macro) that you use in foo.cc <i>that is not declared in foo.cc</i>, either foo.cc or foo.h should #include a .h file that exports the declaration of that symbol.&quot;<p>Not having that phrase tripped me up for a few minutes. I guess everyone else thinks it&#x27;s implied, but for some reason that wasn&#x27;t clear to me until I read through more of their documentation.