Tweak semantics

src/epub/text/chapter-4.xhtml

@@ -64,7 +64,7 @@
 				<p>For <b>Speaking</b>:⁠—Wind the Clockwork Man under his right arm, (marked <abbr>No.</abbr> 2.)</p>
 				<p>For <b>Walking</b> and <b>Action</b>:⁠—Wind Clockwork in the middle of his back, (marked <abbr>No.</abbr> 3.)</p>
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-					<p><abbr>N. B.</abbr>⁠—This Mechanism is guaranteed to work perfectly for a thousand years.</p>
+					<p><abbr epub:type="z3998:initialism">N.B.</abbr>⁠—This Mechanism is guaranteed to work perfectly for a thousand years.</p>
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 			<p>“Well, I declare!” gasped the yellow hen, in amazement; “if the copper man can do half of these things he is a very wonderful machine. But I suppose it is all humbug, like so many other patented articles.”</p>