diff --git a/e-invoice-domain/src/main/kotlin/net/codinux/invoicing/model/codes/CodeLists.md b/e-invoice-domain/src/main/kotlin/net/codinux/invoicing/model/codes/CodeLists.md
index c75b522..8509dad 100644
--- a/e-invoice-domain/src/main/kotlin/net/codinux/invoicing/model/codes/CodeLists.md
+++ b/e-invoice-domain/src/main/kotlin/net/codinux/invoicing/model/codes/CodeLists.md
@@ -26,39 +26,55 @@ Sources of Code Lists according to XRechnung specification p. 105, enhanced by i
 | MIME         | Mime type codes — Mime codes; code list only in EN Excel file                                      |         |                                               | subset    | BT-125-1                                                                |
 
 
-## Einschätzung zu Quellen
+### Where to find
 
-### EN / CEF Genericode Code Listen
+All **UNTDID code lists** can be found at https://unece.org/fileadmin/DAM/trade/untdid/d16b/tred/tredXXXX.htm, where XXXX is the four-digit number from above's table, e.g.,
+
+https://unece.org/fileadmin/DAM/trade/untdid/d16b/tred/tred1001.htm
+
+The **UN/EC Recommendation Nº20 and Nº21** can be found at:
+
+https://unece.org/trade/uncefact/cl-recommendations
+
+
+
+## Evaluation of sources
+
+Usually it's not necessary to parse above's sources directly, there are already compilations of these, which also contain only the required values for EN16931: 
+
+### EN / CEF Genericode Code Lists
 
 URL: https://ec.europa.eu/digital-building-blocks/sites/display/DIGITAL/Registry+of+supporting+artefacts+to+implement+EN16931
 
+It Contains almost all of the above's code lists, even though some additional data is missing.
+
 \+ good to parse
 
 \- no descriptions
 \- only English names
 
 
-### UNTDID
-
-URL e.g.: https://unece.org/fileadmin/DAM/trade/untdid/d16b/tred/tred1001.htm
-
-\+ incl. Engl. descriptions
-
-\- difficult to parse, plain text only (on a website!)
-\- only English names and descriptions
-\- partially more codes than XRechnung standard allows
-
-
 ### Factur-X / ZUGFeRD Code Lists .xslx
 
 Download .zip from: https://www.ferd-net.de/standards/zugferd-2.3.2/zugferd-2.3.2.html?acceptCookie=1
 
-\+ alle code lists in one file
-\+ incl. Engl. descriptions and invoice fields in which codes are used
+\+ all code lists in one file
+\+ incl. English descriptions and invoice fields in which codes are used
 
 \- difficult to parse
 
 
+### UNTDID
+
+URL e.g.: https://unece.org/fileadmin/DAM/trade/untdid/d16b/tred/tred1001.htm
+
+\+ incl. English descriptions
+
+\- difficult to parse, plain text only (on a website!)
+\- only English names and descriptions
+\- partially more codes than XRechnung standard allows
+
+
 ### UNECE Rec. 20 & 21
 
 Recommendation 20 Codes for Units of Measure Used in International Trade
@@ -68,8 +84,15 @@ Recommendation 21 Codes for Passengers, Types of Cargo, Packages and Packaging M
 URL: https://unece.org/trade/uncefact/cl-recommendations
 
 \+ good to parse
-\+ incl. Engl. descriptions
+\+ incl. English descriptions
 \+ incl. unit symbols
 
 \- only units, no other code lists
-\- only English names and descriptions
\ No newline at end of file
+\- only English names and descriptions
+
+
+## Generation
+
+Most of the Code List enums in this folder are generated by [CodeGenerator](../../../../../../../../../e-invoice-spec-parser/src/main/kotlin/net/codinux/invoicing/parser/CodeGenerator.kt) in project `e-invoice-spec-parser`.
+
+It uses the code lists provided by ZUGFerd and the EN / CEF Genericode Code Lists.
\ No newline at end of file