Hello,
So I've run into this case when the plugin crashes on clicking scramble, the input file not being compliant (missing metadata element in opf)
Code:
for child in [e for e in self.eb.opf_xpath('//opf:metadata')[0]]:
(IndexError: list index out of range)
dunno if you're willing to fix this since it's an edge case, but it might be better to add a try except handling just in case things go south unpredictably.