If you've used repository groups in Nexus, you may have run into the issue where you see an artifact in a repository group and wonder "where did this artifact come from?"  In other words you would like to know which real (hosted) repository is actually storing the artifact.  Nexus allows you to see this and other debugging information with a spcial query at the end of the URL.  Just append "?describe" to the end of the URL of the file you are looking at.  For example, if you are looking at the jboss parent pom in the public repository group, and you want to see where it came from, the URL looks like this

https://repository.jboss.org/nexus/content/groups/public/org/jboss/jboss-parent/5/jboss-parent-5.pom?describe

The output is not well formatted, so it's a bit hard to read.  But if you look carefully you can find a field called "originatingRepositoryId" and this points to the "releases" repository.