The same as in editing XML documents, the message of an error obtained by validation of an XML Schema document includes a specification reference to the W3C specification for XML Schema. An error message contains an Info field that when clicked will open the browser on the "XML Schema Part 1:Structures" specification at exactly the point where the error is described thus allowing you to understand the reason for that error.
Validation of an XML Schema containing a type definition with a minOccurs or maxOccurs attribute having a value larger than 256 limits the value to 256 and issues a warning about this restriction in the Message panel at the bottom of the <oXygen/> window. Otherwise for large values of the minOccurs and maxOccurs attributes the validator fails with an OutOfMemory error which practically makes <oXygen/> unusable without a restart of the entire application.