src/vs/workbench/contrib/customEditor/browser/customEditorInput.ts/CustomEditorInput/capabilities
class CustomEditorInput:	public override get capabilities(): EditorInputCapabilities {
		let capabilities = EditorInputCapabilities.None;

		if (!this.customEditorService.getCustomEditorCapabilities(this.viewType)?.supportsMultipleEditorsPerDocument) {
			capabilities |= EditorInputCapabilities.Singleton;
		}

		if (this._modelRef) {
			if (this._modelRef.object.isReadonly()) {
				capabilities |= EditorInputCapabilities.Readonly;
			}
		} else {
			if (this.fileService.hasCapability(this.resource, FileSystemProviderCapabilities.Readonly)) {
				capabilities |= EditorInputCapabilities.Readonly;
			}
		}

		if (this.resource.scheme === Schemas.untitled) {
			capabilities |= EditorInputCapabilities.Untitled;
		}

		return capabilities;
	}