I usually create my HTML files in Dreamweaver. I've been using it for years so it is my "comfort" app when it comes to creating multiple HTML files that are linked to one another for a larger document (or a web site). I like to use HTML 5, not XHTML. I've noticed that Sigil has always converted my HTML 5 files into XHTML whenever I import them. I haven't found a way around that, but to be honest I haven't looked very much either!

If I'm going to create a large document/book that will be published, this is my actual workflow:

• Create the HTML 5 and CSS files in Dreamweaver, including a stand-alone TOC.
• Use Dreamweaver to organize the book.
• Use Dreamweaver to incorporate any image files.
• Start Sigil and import all my HTML, CSS, images, etc.
• Use Sigil to designate a cover.
• Use Sigil to edit the metadata.
• Use Sigil to create a TOC, internal file structure.
• Create the ePub in Sigil.
• Copy the ePub file to a working folder.
• Rename myBookName.epub to myBookName.zip then unzip the file.
• In the unzipped folder that was the ePub, I replace all the XHTML files created in Sigil with the HTML 5 files I originally created in Dreamweaver. This gets rid of the stuff Sigil added or changed as for as ML goes.
• Edit the toc.ncx and ensure all the file name references are correct and add or correct the references for the cover and TOC in accordance to Amazon's guidelines for creating KF8.
• Use Kindle Previewer to compile the files into a KF8/mobi book.

I know this looks rather convoluted and complex, but it really isn't. Dreamweaver is the main development tool. Sigil lets me take my book files and generate a clean ePub. Sigil does a good job with the toc.ncx file, and trust me you don't want to have to create one of those by hand! Since Amazon's specs for clean KF8 are a little different from those of an ePub, it is back to Dreamweaver to clean up the files before finally using Kindle Previewer to compile the files into a KF8/mobi. As a result I seem to consistently create trouble free books.

If I'm merely creating a document solely for my own use, I won't go to this much trouble.