Does Head evaluate its argument?

[#1]

From Using JSL to Develop Efficient, Robust Applications (EU 2018 415), I learned that there are some functions which evaluate their argument and others which don't:

I wondered about Head. Here everything looks logic ...

f= Expr(x=2);
Substitute(NameExpr(f),Expr(x), Expr(y));
Head(f);

Head is not like Substitute, I can directly use the function name as an argument  - and Head returns the head of the expression: Assign() 

After checking some other functions which "don't evaluate their argument":

Expr(x=2); // x=2
Name Expr(x=2); // x=2

let's check the result for

Head(x=2)

which is "2" - i.e. the result after evaluating the argument?!?! why is it not assign()?

[#2]

#ExpressionInspector