The ReplaceChild(spec, xmlTree) command replaces a specific child of an XML document tree with new content.

The first argument is an equation whose left-hand side specifies which child to replace, and whose right-hand side is the replacement content. The syntax mimics that of subsop. A new XML document tree is returned with the replacement content appearing instead of the child element specified in the left-hand side of the first argument.

$\mathrm{with}\left(\mathrm{XMLTools}\right)\:$

$\mathrm{doc}≔\mathrm{XMLElement}\left(''a''\,\left[\right]\,\mathrm{XMLElement}\left(''b''\,\left[''colour''=''red''\right]\,''foo''\right)\,\mathrm{XMLElement}\left(''c''\,\left[''colour''=''blue''\right]\,''bar''\right)\,\mathrm{XMLElement}\left(''d''\,\left[\right]\,''baz''\right)\right)\:$

$\mathrm{Print}\left(\mathrm{doc}\right)$

<a>
  <b colour = 'red'>foo</b>
  <c colour = 'blue'>bar</c>
  <d>baz</d>
</a>

$\mathrm{Print}\left(\mathrm{ReplaceChild}\left(2=\mathrm{XMLElement}\left(''NEW''\&comma;\left[\right]\&comma;''text''\right)\&comma;\mathrm{doc}\right)\right)$

<a>
  <b colour = 'red'>foo</b>
  <NEW>text</NEW>
  <d>baz</d>
</a>