We have in [expr.const]/4:

A constant-initialized potentially-constant variable is usable in constant expressions at a point P if its initializing declaration D is reachable from P and

• (4.1) it is constexpr,
• (4.2) it is not initialized to a TU-local value, or
• (4.3) P is in the same translation unit as D.

There are a lot of nouns here. Which one of them does "it" refer to? I'm guessing the variable, but that takes a bit to work out, and the variable isn't even the closest noun to "it" where it is being used.

Suggestion:

A constant-initialized potentially-constant variable V is usable in constant expressions at a point P if its V's initializing declaration D is reachable from P and

• (4.1) it V is constexpr,
• (4.2) it V is not initialized to a TU-local value, or
• (4.3) P is in the same translation unit as D.