[xml] xmlSchemaValidateDoc: return value -1 ?

[<j s bach o2online de>]

Hello all,

I have a valid xsd and xml which i can validate with xmllint tool:
jsbach orgel:[~/cp_comModell/lib/xml] > xmllint --noout --schema processor.xsd enhanced_processor.xml     
enhanced_processor.xml validates


Now if i use xmlSchemaValidateDoc(schema_valid_ptr, doc), it  delivers a -1 on validating.. Does this mean it 
was successfull?  I've looked at the example of the implementor of the schemas in libxml, he doesn't use the 
return value there at all..
http://mail.gnome.org/archives/xml/2005-January/msg00192.html

output from my prog:
jsbach orgel:[~/cp_comModell/src] > ./pscheme ../lib/xml/processor.xsd ../lib/xml/enhanced_processor.xml
schema validation return value: -1

Is -1 thought for successfull validation? Can you put a bit doc at least on what should be 
expected for return values?