The relevant ECMA standards are full of crazy bullshit that, to the best of my knowledge, nobody has ever implemented in any hardware or software terminal, like control sequences to make lines of text run vertically (SPD), or to fully justify text (JFY), or to use a Fraktur font (SGR 20). They're also incomplete -- they go into very little detail explaining what various control sequences should do, especially in exceptional circumstances, and they don't discuss Unicode at all (as they haven't been updated since the early 1990s).
Good to see you've added support for that but the cynic in me can't help wondering if that ANSI code is even needed. While you're right that unicode makes it easy to support, it's also even easier to output the Fraktur characters directly from the CLI application and do away with that particular escape code entirely. The bonus in doing that is you then support more terminals in the process since unicode is more widely supported than the Fraktur escape sequence.
This isn't me being critical in what you've done though. More of an adjacent commentary about the state of ANSI escape sequences.
