Just to be absolutely clear, when I say "empty span tags" I mean span tags that have
nothing inside them -- no classes, style or any other attributes. Example below:
Code:
<h1 class="heading"><span>CHAPTER 1</span></h1>
Whereas "a naked span tag" I think refers to a span tag containing perhaps some attributes as well as text on it's own line in the html that is not surrounded by any other html tags. That's my understanding of "naked spans" anyway. As well, "naked spans" surrounding text or whatever can also contain classes and other attributes.
Generally, as a rule, I always try and avoid using both "empty span tags" and "naked span tags" in my own epubs. In most instances, empty spans serve no earthly purpose and naked spans alone and on their own line(and not surrounded by <div> tags) will always give you an error whenever you run FlightCrew or Epubcheck.