It might be, that I'm missing something, because formal language definition is somewhat new to me, but right now it seems to me, that a statement can never generate a simple expression like $v = 1.

A statement can generate an expression statement, which can generate an expression.

expression-statement: expressionopt ; 

But I can't find any way to generate a primary-expression or an assignment-expression out of an expression. When searching the repository for the terms, I can only find their definitions, not any usages of them: repository search for 'primary-expression'

What am I missing here?