Beyond the reserved words, also rejects names that exist as values and break when rebound.

Whether a name is spelled as a JavaScript identifier. Written on the characters rather than through String.front for the reason isReserved is: the reader in Parse has to be shown that a name the compiler let through is one it can read back, and that argument reads the characters.

Every helper in the generated code starts with __. The prefix is reserved so that user names cannot collide with them.

The same test as String.startsWith reservedPrefix, written on the characters so that it reduces: the generated code's helper dispatch is guarded by it, and a proof about a call has to see that a name the compiler let through is not a helper.

The prefix a declaration's unchecked body is named under. Inside the reserved prefix, so nothing a program can write reaches it, and no runtime helper carries a _ in that position, so the two names the compiler writes stay apart from each other as well as from the ones it is given.

The function a call from inside the package lands on: the declaration's body with no entry check in front of it. The declared name stays with the checked function a consumer imports.

The same test as String.startsWith bodyPrefix, written on the characters for the reason isReserved is: the helper dispatch and the environment both have to be shown that a name is or is not one of these, and those arguments read the characters.

A name the compiler was given is never a body name: validateIdent rejects the whole reserved prefix, and the body prefix is inside it.

Nothing that passed the check carries the helper prefix, which is what keeps a compiled name from colliding with one the compiler introduces itself.

Nothing that passed the check is spelled as anything but an identifier, which is what lets the reader in Parse take a compiled name back.