Before revision: Most frequently, there is a primary sub-code that identifies the language (e.g., "en"), and an optional sub-code in capital letters that specifies the national variety (e.g., "GB" or "US" according to ISO 3166-1 alpha-2).
After revision: Most frequently, there is a primary subcode that identifies the language (e.g., "en"), and an optional subcode in capital letters that specifies the national variety (e.g., "GB" or "US" according to ISO 3166-1 alpha-2).