The Accordion navigator displays its children as a set of expanding
panels, stacked one above the other. Each child has a header
button created for it that can be clicked to expand the child to make
it visible. Only one child can be visible at any time, so expanding a
new child minimises the child that was previously selected.
The user can click any of the header buttons to select the
corresponding child, which expands that child and minimises the
previously selected child.
Of course, the same effect can be achieved with Ajax but that relies
on Javascript being enabled in the user’s browser.
The accordion properties can be updated using CSS generated by
the Flex style explorer in this
Adobe site.