Expander doesn't work on subsequent clicks - once it's collapsed, it won't open again. If the hidden attribute is set initially (it’s necessary as content collapsed by default in only hidden visually and not to screen readers - something to be added to the docs?), it won't open at all.
Reproducible on https://docs.atlassian.com/aui/9.0.0/docs/expander.html examples.
Steps to reproduce
Usage described in documentation
Demonstration of all states
Interactive state (screen readers)
Visual regression tests
Navigation (only keyboard / only mouse)
Component render legibly
Element status (At Rest/Pressed/Selected/Read Only/Disabled)