code switching

A colleague writes to ask:

I read your article ‘Code Switching’ in Sociocultural Linguistics. What I wonder is [why] you didn’t write something about the author Grosjean (1982, Life with Two Languages). He also used the term Code Switching as one of the first. And I can’t get the differences between ‘ language alternation’ and ‘ code switching’? Can you describe the differences?

These are excellent questions.