The interface "DiagnosticClientCapabilities" as defined both in _specifications/lsp/3.17/language/pullDiagnostics.md and _specifications/lsp/3.18/language/pullDiagnostics.md refers to a type named ClientDiagnosticsTagOptions. The latter type, however, is nowhere defined in the Markdown documents!
It can be found, though, in _specifications/lsp/3.18/metaModel/metaModel.json . While I am not sure whether this is intended, I think it would be a good idea to add the definition of ClientDiagnosticsTagOptions to the pullDiagnostics.md document, as well, so that it also appears in the online-documentation at https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/