639-3 for cases where none of the specific codes are appropriate. These are intended primarily for applications like databases where an ISO code is required regardless of whether one exists. (uncoded languages, originally an abbreviation for 'miscellaneous') is intended for languages which have not (yet) been included in the ISO standard. (multiple languages) is intended for cases where the data includes more than one language, and (for example) the database requires a single ISO code. (undetermined) is intended for cases where the language in the data has not been identified, such as when it is mislabeled or never had been labeled. It is not intended for cases such as Trojan where an unattested language has been given a name. (no linguistic content / not applicable) is intended for data which is not a language at all, such as animal calls. In addition, 520 codes in the range – are 'reserved for local use'. For example, Rebecca Bettencourt assigns a code to constructed languages, and new assignments are made upon request. The Linguist List uses them for extinct languages. Linguist List has assigned one of them a generic value: , unnamed proto-language. This is used for proposed intermediate nodes in a family tree that have no name. Maintenance processes The code table for ISO 639-3 is open to changes. In order to protect stability of existing usage, the changes permitted are limited to: modifications to the reference information for an entry (including names or categorizations for type and scope), addition of new entries, deprecation of entries that are duplicates or spurious, merging one or more entries into another entry, and splitting an existing language entry into multiple new language entries. The code assigned to a language is not changed unless there is also a change in denotation. Changes are made on an annual cycle. Every request is given a minimum period of three months for public review. The ISO 639-3 Web site has pages that describe "scopes of denotation" (languoid types) and types of languages, which explain what concepts are in scope for encoding and certain criteria that need to be met. For example, constructed languages can be encoded, but only if they are designed for human communication and have a body of literature, preventing requests for idiosyncratic inventions. The registration authority documents on its Web site instructions made in the text of the ISO 639-3 standard regarding how the code