It's a shame that the list is in that order (both on the htmx website and in the book). Items 1 and 3 are simply not important, whereas 4 is by far the most important feature that HTMX offers.
from the book:
> This gives us our fourth, final and perhaps most important opportunity to generalize HTML: Opportunity 4
> HTML could be extended to allow the responses to requests to replace elements within the current document, rather than requiring that they replace the entire document.
> This is actually a very old concept in hypermedia. Ted Nelson, in his 1980 book “Literary Machines” coined the term transclusion to capture this idea: the inclusion of content into an existing document via a hypermedia reference. If HTML supported this style of “dynamic transclusion,” then Hypermedia-Driven Applications could function much more like a Single Page Application, where only part of the DOM is updated by a given user interaction or network request.