const plugin: LanguageServicePlugin = {
	capabilities: {
		diagnosticProvider: {
			workspaceDiagnostics: true,
		},
	},
	create(context): LanguageServicePluginInstance<Provide> {
		return {
			provideWorkspaceDiagnostics() {
				return [{
					uri: 'file://a.css',
					items: [{
						severity: 2,
						source: 'html1',
						message: 'Only one style tag is allowed.',
						// ...
					}]
				}];
			}
		};
	},
}