<style>
body {
  margin: 0px;
  font-family: ahem;
  font-size: 20px;
}

div {
  width: 10px;
}

.test {
  word-break: break-all;
  color: red;
}

.ref {
  word-break: normal;
  color: green;
  position: absolute;
  top: 0px;
}
</style>
<!-- do not break between punctuation, but break at other positions -->
<div class=test>X !!!should_break</div>
<div class=ref>X !!! s h o u l d  _ b r e a k</div>
