Values

Four forms are different. Do not treat them as the same string.

KEY: "value";

A literal. Vidro owns the value.

KEY;

Required, and not yet given a literal or an external source. This is not an empty string.

KEY: "";

An explicit empty string.

KEY: $KEY;

An external reference. For now the name on both sides is the same. See External Values.

website.development {
  API_URL: "http://localhost:8080";
  REQUIRED_KEY;
  EMPTY_KEY: "";
}

API_URL is a literal, REQUIRED_KEY is unresolved, and EMPTY_KEY is empty on purpose.