To edit it. I-EPUB yi-XHTML ephindayo kwi-zip - umbhalo uphinda- ubekwe- ngaphandle nakweyiphi na ububanzi bekhusi, oko kukuthi kutheni abafundi be-e- bakhetha oku, which is optimised for reading rather than revising; a document format is what you need to make changes, add comments, run a word count or hand the manuscript to an editor.