What standard clause mandates this lvalue-to-rvalue conversion?

Given:

int main() {
   int x = 0;
   int y = x; // <---
}

Could someone please tell me which clause of the standard (2003 preferred) mandates the conversion of the expression x from lvalue to rvalue in the initialisation of the object y?

(Or, if I'm mistaken and no such conversion takes place, then I'd like to learn that too!)