@Override
    public Object execute(EventExecuteCommandContext context) {
        if (fileURI == null)
            return null;
        // No return value, as the execution **is** issuing an action on the client side.
        context.messageHandler.showDocument(fileURI).join();
        return null;
    }
OpenDocument
Kind of a reflection: client sends "Open document with fileURI", and server responds by telling the client to open it.
Reason for this: Used in Code Actions to make file automatically open with new edit.
integration/schema-language-server/language-server/src/main/java/ai/vespa/schemals/lsp/common/command/commandtypes/DocumentOpen.java