'How replace text with DOMDocument

Need change letter "a" to "1" and "e" to "2"

This is approximately html, in fact it is more nested

<body>
  <p>
    <span>sppan</span>
    <a href="#">link</a>
    some text
  </p>
  <p>
    another text
  </p>
</body>

expected output

<body>
  <p>
    <span>spp1n</span>
    <a href="#">link</a>
    some t2xt
  </p>
  <p>
    anoth2r t2xt
  </p>
</body>

Sources

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Solution	Source