src/vs/workbench/browser/parts/editor/editorGroupView.ts/EditorGroupView/doCloseInactiveEditor
class EditorGroupView:	private doCloseInactiveEditor(editor: EditorInput, internalOptions?: IInternalEditorCloseOptions): number | undefined {

		// Update model
		return this.model.closeEditor(editor, internalOptions?.context)?.editorIndex;
	}