A <ul> is a list of things whose order makes no difference to its meaning. Rearranging a <ul> would change the presentation, not the information. Rearranging an <ol> would change both.
reply <ul> Players
<li> Alice
<li> Bob
<li> Carol
</ul>
<ol> Leaderboard
<li> Bob
<li> Alice
<li> Carol
</ol>Too late to edit now, but I should mention putting titles in a list like that isn't valid. It's just to shorten the example.
replyExactly. “Unordered” implies “reordering doesn’t change meaning.” And yet that’s already implicit in the bullets (vs numbers).
replySo is it a decoration hint? Or is it actually semantic? And what system is interpreting the semantics rather than the visual presentation?
HyperText Markup Language is semantic. You're marking up a document to show what information it contains, where it contains it, and how it relates to other documents or information. Reading markup causes browsers to display things, but that's incidental.
replyIn theory.
In practice, no one cares about semantics and the tags are chosen based on how a target set of browsers happens to display them.