How to put an annotation in HTML?

Sorry, probably a stupid questions:

Let us say, I have some HTML like this...

<p>It is well known, that Springfield has mild summers and short, but hard
winters.</p>

And now, for example in order to simplify extraction, I want to annotate
Springfield with an URI, maybe like this, to make sure that the computer
understands I mean the Springfield in Massachusetts:

<p>It is well known, that <span
about="http://sws.geonames.org/4951788/">Springfield</span>
has mild summers and short, but hard winters.</p>

How do I actually do that?

Mind you, I don't want to add whole triples, but just annotate the HTML and
say "this element refers to the following URI".

Cheers,
Denny


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