1 Introduction  
2 Background  
2.1 Related Work  
2.2 History of XAI  
2.3 Basic Definitions  
3 Approach to Literature Search  
3.1 Search  
3.2 Categorization  
3.3 Results  
4 A Survey of Surveys on XAI Methods and Aspects  
4.1 Conceptual Reviews  
4.2 Broad Method Collections  
4.3 Method Collections with Specific Focus  
4.4 Toolboxes  
5 Taxonomy  
5.1 Problem Definition  
5.2 Explanator  
5.3 Metrics  
6 Discussion and Conclusion