Clean, Simple and Portable. It's exactly like HTML Page, complete (*.html), the differemve is that all files are bundled into a ZIP file which has the extension HTMLZ. It's so simple that I wonder why the creators of defunct MAF/MAFF didn't think about it many years ago http://maf.mozdev.org/maff-file-format.html Untile a week ago, Wikimedia supported exporting pages into HTMLZ.
I correct myself: Clean, Simple, Portable and Manageable (e.g. editing CSS and JS files, which is easier to handle than MHTML). Don't get me wrong. I like the MHTML format and I use it excessively. HTMLZ is good too.
I apologies for double posting. The following is an indication for support of htmlz by wikimedia (third line below) https://github.com/wikimedia/ws-export/blob/d95595b29dd9c1a7c4b0636bf40261f6a9879b54/i18n/qqq.json#L37 "format-epub-3": "Format label and description.", "format-epub-2": "Format label and description.", "format-htmlz": "Format label and description.", "format-mobi": "Format label and description.", "format-pdf-a4": "Format label and description.", "format-pdf-a5": "Format label and description.", "format-pdf-a6": "Format label and description.", "format-pdf-letter": "Format label and description.", "format-rtf": "Format label and description.", "format-txt": "Format label and description.", For some reason, which doesn't seem to be publicly announced, the support for export to non-PDF formats isn't available, perhaps because of pressure or nepotism of big business or perhaps that wiki foundation has decided to be less productive.
Read The Docs also provides HTMLZip files https://readthedocs.org/projects/i2pd/downloads/