oai-pmh.md

-What is OAI-PMH and where to find information?
+## What is OAI-PMH and where to find information?
 The Open Archives Initiative - Prototcol for Metadata Harvesting provides an application-independent interoperability framework. 
 The details can be found: 
 [http://www.openarchives.org] (http://www.openarchives.org/OAI/openarchivesprotocol.html)
 
+## Online Validation
 Useful online tool for validation:
 [https://validator.oaipmh.com/](https://validator.oaipmh.com/)
+Hint: The Standard says "The Content-Type returned for all OAI-PMH requests **must** be _text/xml_." but the validator expect _application/xml_!