php/simplexml adding elements before and after text

I'm trying to insert elements into an xml document around some text. Part of the problem may be that this is not well-formed xml and it needs to be easier to read for a human as plain text. So what I have is something like this:

<record>
  <letter>
    <header>To Alice from Bob</header>
    <body>Hi, how is it going?</body>
  </letter>
</record>

I need to end up with this:

<record>
  <letter>
    <header>To <to>Alice</to> from <from>Bob</from></header>
    <body>Hi, how is it going?</body>
  </letter>
</record>

Something similar should be valid html:

<p>To <span>Alice</span> from <span>Bob</span></p>

I can set the value of the header to a string, but the <> are converted to &lt and &gt, which is no good. Right now I'm using $node->header->addChild('to', 'Alice') and $node[0]->header = 'plain text'.

If I do

$node->header->addChild('to', 'Alice'); 
$node->header = 'plain text';
$node->header->addChild('from', 'Bob');

Then I get

<header>plain text <from>Bob</from></header>

The 'to' is wiped out.

Quick and dirty ways are to just let it be

<header>plain text <to>Alice</to><from>Bob</from></header>

And then just open the file a second time and move the elements around. Or search and replace the &lt and &gt. That seems the wrong way though.

Is this possible with simpleXML?

Thank you!

Solution

From the viewpoint of DOM (and SimpleXML is an abstraction on top of that), you're do not insert elements around text. You replace a text nodes with a mix of text nodes and element nodes. SimpleXML has some problems with mixed child nodes, so you might want to use DOM directly. Here is a commented example:

$xml = <<<'XML'
<record>
  <letter>
    <header>To Alice from Bob</header>
    <body>Hi, how is it going?</body>
  </letter>
</record>
XML;

// the words and the tags you would like to create
$words = ['Alice' => 'to', 'Bob' => 'from'];
// a split pattern, you could built this from the array
$pattern = '((Alice|Bob))';

// bootstrap the DOM
$document = new DOMDocument();
$document->loadXml($xml);
$xpath = new DOMXpath($document);

// iterate any text node with content
foreach ($xpath->evaluate('//text()[normalize-space() != ""]') as $text) {
  // use the pattern to split the text into an list
  $parts = preg_split($pattern, $text->textContent, -1, PREG_SPLIT_DELIM_CAPTURE);
  // if it was split actually
  if (count($parts) > 1) {
    /// iterate the text parts
    foreach ($parts as $part) {
      // if it is a word from the list
      if (isset($words[$part])) {
        // add the new element node
        $wrap = $text->parentNode->insertBefore(
          $document->createElement($words[$part]),
          $text
        );
        // and add the text as a child node to it
        $wrap->appendChild($document->createTextNode($part));
      } else {
        // otherwise add the text as a new text node
        $text->parentNode->insertBefore(
          $document->createTextNode($part),
          $text
        );
      }
    }
    // remove the original text node
    $text->parentNode->removeChild($text);
  }
}

echo $document->saveXml();

Output:

<?xml version="1.0"?>
<record>
  <letter>
    <header>To <to>Alice</to> from <from>Bob</from></header>
    <body>Hi, how is it going?</body>
  </letter>
</record>