In the overview of the Accordion, under the heading Theming, the following sentence appears:
The active header will additionally have a ui-accordion-content-active class, the inactive headers will have a ui-accordion-header-collapsed class.
This incorrectly references 'content' that should be 'header'.
Correct:
The active header will additionally have a ui-accordion-header-active class, the inactive headers will have a ui-accordion-header-collapsed class.