<!DOCTYPE html>
<!--
 | Wrapping is only performed at an allowed break point, called a soft wrap
 | opportunity. In most writing systems, in the absence of hyphenation a soft
 | wrap opportunity occurs only at word boundaries. However, when the
 | word-wrap property has a value of break-word, unbreakable "words" may be
 | broken at an arbitrary point to prevent overflow, while still preserving
 | grapheme clusters.
 |   https://www.w3.org/TR/css3-text/#soft-wrap-opportunity
 |   https://www.w3.org/TR/css-text-3/#line-break-details
 |   https://www.w3.org/TR/css-text-3/#word-wrap
 |
 | When no soft wrap location can be found and break-word is allowed, the last
 | grapheme cluster boundary that can fully fit within the width will be
 | selected.
 -->
<html>
<head>
  <style>
    body {
      margin: 0px;
      font-family: Roboto;
      font-size: 20px;
    }
    .containing-block {
      background-color: #03a9f4;
      width: 100px;
    }
    .word-wrap-break-word {
      word-wrap: break-word;
    }
    .word-wrap-normal {
      word-wrap: normal;
    }
  </style>
</head>
<body>
  <div class="containing-block">
    <div class="word-wrap-break-word"><span>abcd<span class="word-wrap-normal">efgh</span>ijkl</span></div>
    <div class="word-wrap-normal"><span>abcd<span class="word-wrap-break-word">efgh</span>ijkl</span></div>
    <div class="word-wrap-normal"><span><span class="word-wrap-break-word">abcd</span><span>efgh</span>ijkl</span></div>
    <div class="word-wrap-normal"><span>abcd<span>efgh</span>ijkl</span></div>
  </div>
</body>
</html>