Interesting. I added a span with a id to a test epub and then converted it from epub to epub. Not only was a span with an id not removed, it had a class added. My theory about the spans being removed seems to have been shot down. Calibre 3.25, BTW.
Original epub:
Code:
<body class="epub">
<p class="paranon"><span id="tarfu_1.3">This is a sample ebook with a few lines of text though it's hard to say what is actually a line of text when font size, screen width, margin size are variables beyond the control of the author. Of course, we could go to absolute measurements if we really want odd effects. EOT</span></p>
</body>
Converted epub:
Code:
<body class="epub">
<p class="paranon"><span id="tarfu_1.3" class="calibre">This is a sample ebook with a few lines of text though it's hard to say what is actually a line of text when font size, screen width, margin size are variables beyond the control of the author. Of course, we could go to absolute measurements if we really want odd effects. EOT</span></p>
</body>
The added class:
Code:
.calibre {
line-height: 1.2
}