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    body { font-family: 'Ahem'; color:green }
    .hang { text-indent: -1em; margin:1em }
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<div style="float:left" class="hang">(Hang test)</div>
<div style="clear:both">
<div class="hang">(This should hang.<br>(This should not.</div>
<div class="hang" style="text-align:justify; width:300px;">(This should hang and justifybecause and now were fine.</div>
<div class="hang" style="text-align:justify; width:300px;"><span>(</span>This should hang.</div>
<div style="margin-left:1em; text-align:justify; width:300px;"><span style="border-left:1em solid blue">(</span>This should not hang.</div>
<div class="hang" style="text-indent:1em; text-align:justify; width:300px;">(This should hang into the text-indent.</div>