Thank you for the PR, but this change breaks a lot of unit tests (see the CI build failure), so can you look at that and see what you need change in the code to ensure they still work, please?

I'm also not sure what the bug is here. Could you explain to which methods or requests you want to pass in a string to this structure, rather than controlling the encoding of it to an array yourself? I'm thinking that such encoding could make more sense in the wrapping methods in the X objects (Display, Window etc), rather than this low down in the protocol implementation.