Exactly one 'toc' nav element must be present Multiple occurrences of the 'page-list' nav element Multiple occurrences of the 'landmarks' nav element The span element must only be used as heading for flat sublists (not hierarchical navigation structures) Missing epub:type attribute on anchor inside 'landmarks' nav element Anchors within nav elements must contain text Spans within nav elements must contain text nav elements other than 'toc', 'page-list' and 'landmarks' must contain a heading as the first child Heading elements must contain text