A dependent. Please add references if different.
-->
<style>
@font-face {
  font-family: mplus;
  src: url(/fonts/mplus-1p-regular.woff);
}
.container > div {
  font-family: mplus;
  word-break: auto-phrase;
  font-size: 10px;
  border: 1px solid;
}
</style>
<div class="container" lang="ja">
  <!-- Both phrases can fit to 7em, but the whole sentence doesn't. -->
  <div style="width: 7em">
    楽しいドライブ。</div>
  <!-- The 2nd phrase doesn't fit to `4em`, hence fallback to normal. -->
  <div styl