Performs NCX internal checks:
NCX_PrologPubId
NCX public identifier is "-//NISO//DTD ncx v1.1.0//EN"
NCX_Version
Version attribute on NCX element has value 1.1.0
ncx_metaDtbDepthValueCorrelated
dtb:depth content attribute value indicates depth of structure of the
DTB as exposed by the NCX
Performs NCX relations checks:
ncx_UidOpfUid
dtb:uid value matches package unique-identifier
ncx_manifestRefs
NCX only references files that are items in manifest
ncx_srcSMIL
src attribute on content element references SMIL file
ncx_srcAudio
src attribute on audio element references audio file
ncx_srcImg
src attribute on img element references image file