It was originally intended for language tags, but has now been repurposed as emoji modifiers, specifically for region flags.
U+E0001, U+E0020–U+E007F were originally intended for invisibly tagging texts by language[3] but that use is no longer recommended.
[5] Unicode states that "the use of tag characters to represent language tags in a plain text stream is still a deprecated mechanism for conveying language information about text".
However, as of Unicode version 12.0 only the three flag sequences listed above are "Recommended for General Interchange" by the Unicode Consortium, meaning they are "most likely to be widely supported across multiple platforms".
[8] The following Unicode-related documents record the purpose and process of defining specific characters in the Tags block: