- added info about schema resolution (resolving)

README.md

@@ -41,9 +41,22 @@ Schemas
 </slubschemacatalog>
 ```
 
-
 For a (german) introduction how to use it, check https://www.data2type.de/xml-xslt-xslfo/docbook/xml-kataloge 
 
+Namespace based Schema resolution
+---------------------------------
+
+The schema resolution follows the rules:
+
+1. if schematype is "nonvalidating", the resourceresolver returns null, indicating the validator should ignore rules
+2. if schematype is "schema" and the baseuri is local and the associated systemid is defined, a combined url will be used, pE.
+   - baseUri = file:/tmp/xml_plugin4rosetta/example_catalog/mets-1.12.1/mets.xsd
+   - SystemId = http://www.loc.gov/standards/xlink/xlink.xsd
+   - combined: file:/home/romeyke/git/xml_plugin4rosetta/example_catalog/xlink-1.1/xlink.xsd
+3. if schematype is "schema" then the url of associated namespace will be used
+
+Hint: in case of nonvalidating schemaurl should never be empty!
+
 Copyright hints
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