dnaber-de/dom-dissolve-node.php

## dom-dissolve-node.php
<?php
$html = <<<HTML
<table>
    <tr>
        <td>Foo with some <span>makrup</span> inside</td>
        <td>Bar also <div>with <em>some</em></div> markup</td>
    </tr>
</table>
HTML;

$dom = new DOMDocument;
$dom->loadXML( $html );

// remove the <td>-Tags and keep everything else
$tdList = $dom->getElementsByTagName( 'td' );
while( $tdList->length > 0 ) {
    $td = $tdList->item( 0 );
    $fragment = $dom->createDocumentFragment();
    while( $td->childNodes->length > 0 )
        $fragment->appendChild( $td->childNodes->item( 0 ) );

    $td->parentNode->replaceChild( $fragment, $td );
}

var_dump( $dom->saveHTML() );
/**
 *   string(141) "<table>
 *       <tr>
 *           Foo with some <span>makrup</span> inside
 *           Bar also <div>with <em>some</em></div> markup
 *       </tr>
 *   </table>
 *   "
 */
	<?php
	$html = <<<HTML
	<table>
	<tr>
	<td>Foo with some <span>makrup</span> inside</td>
	<td>Bar also <div>with <em>some</em></div> markup</td>
	</tr>
	</table>
	HTML;

	$dom = new DOMDocument;
	$dom->loadXML( $html );

	// remove the <td>-Tags and keep everything else
	$tdList = $dom->getElementsByTagName( 'td' );
	while( $tdList->length > 0 ) {
	$td = $tdList->item( 0 );
	$fragment = $dom->createDocumentFragment();
	while( $td->childNodes->length > 0 )
	$fragment->appendChild( $td->childNodes->item( 0 ) );

	$td->parentNode->replaceChild( $fragment, $td );
	}

	var_dump( $dom->saveHTML() );
	/**
	* string(141) "<table>
	* <tr>
	* Foo with some <span>makrup</span> inside
	* Bar also <div>with <em>some</em></div> markup
	* </tr>
	* </table>
	* "
	*/