Earlier quoted context omitted.
> If you publish a book as plain HTML scrolling becomes impossible, as any tiny movement will catapult you numerous pages forward. This isn't true on any popular browser or platform. Single-page scrolling using the keyboard, mouse, or touchscreen is built-in for all common browsers and scrolling even extremely large documents has been fine for at least a decade – unless you load it up with tons of JavaScript even in…
> You can't, and also wouldn't want to since that's inherently unstable (e.g. I resize the window slightly and all of the links break). What you can do is what people have been doing since around 1993 and put anchors on logical sections, paragraphs, etc. so you have a linkable stable anchor which doesn't depend on the window or font size. Except there is no way to expose such anchors to the user without cluttering up…
> Except there is no way to expose such anchors to the user without cluttering up the display.
1. Using unobtrusive anchors isn't that bad as far as clutter goes — if you have a discrete octothorpe or paragraph symbol consistently at the start or end of a paragraph it's not the end of the world, especially if they're styled to be in the margin outside of normal text flow.
2. Since approximately late 1995, people have used JavaScript to only display those symbols on hover/focus. This works well and is pretty common around the web.
I'm not saying that there isn't room for improvement such as Chrome's extension but when there's 3 decades of common usage for something you say can't be done it suggests that the probably isn't that it's impossible but that there isn't enough social pressure to make publishers _want_ to publish books as HTML. Examples of massive documents are easy enough to find (e.g. W3C specs) so I'd prefer to spend time thinking about why other people aren't (e.g. DRM) and what you can do about the real problems.