What is the difference between 'disabled' and 'skipped' in Junit4?

I'm trying to build a number of test runners that share a common output format. I'd like to adopt JUnit4 as the output standard, and found several XSDs for it. (including a well? documented version from here: JUnit XML format specification that Hudson supports)

All of these XSDs agree that there is BOTH a 'skipped' and 'disabled' attribute on the 'testsuite' element, but i have never seen any XML that has both these values...

I also searched the JUnit website, where they seem to conflate 'disabled' with 'ignored' (http://ift.tt/2uCzKiJ).

If a test explicitely marked to be ignored (e.g. @Ignore) is called 'disabled' in the output, what is 'skipped' for and when should i use it?