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    .hang { hanging-punctuation: allow-end; margin:1em; width:5em; border:2px solid black }
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<div style="float:left; width:auto" class="hang">12 34,</div>
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<div class="hang">12 34,<span></span> 1234,</div>
<div class="hang">12 34,<span style="border-left:1em solid black"></span> 1234,</div>
<div class="hang">12 34,<span style="border-right:1em solid black"></span> 1234,</div>
<div class="hang"><span style="border-right:1em solid black">12 34,</span> 2345</div>
<div class="hang">12 34<span style="border-left:1em solid black">,</span> 2345</div>