[1] 
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#signatureInformation

[2] 
https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/progmodes/eglot.el?id=fa669c4b17c04eff852eb23a6179ccb8fab864db#n3132