Bad practice to declare names in the standard namespace?

Question

I was looking through the Google C++ style guide, and came across this:

\"Do not declare anything in namespace std, not even forward declarations of standard library

Answer 1

They're saying that you shouldn't forward declare stuff from the standard library like this:

// myheader.h
namespace std{
template
void SomeStandardFunction();
}

// use std::SomeStandardFunction

Instead, you should just include the header directly:

// myheader.h
#include 

// use std::SomeStandardFunction