从嵌套元素中删除不需要的文本

我有以下xml文档:

<?xml version="1.0" encoding="UTF-8"?>
<header level="2">My Header</header>
<ul>
    <li>Bulleted style text
        <ul>
            <li>
                <paragraph>1.Sub Bulleted style text</paragraph>
            </li>
        </ul>
    </li>
</ul>
<ul>
    <li>Bulleted style text <strong>bold</strong>
        <ul>
            <li>
                <paragraph>2.Sub Bulleted <strong>bold</strong></paragraph>
            </li>
        </ul>
    </li>
</ul>

我需要删除子项目符号文本前面的数字。 1。和2。在给定的示例中

这是我到目前为止的代码:

<?php
class MyDocumentImporter
{
    const AWKWARD_BULLET_REGEX = '/(^['s]?['d]+['.]{1})/i';
    protected $xml_string = '<some_tag><header level="2">My Header</header><ul><li>Bulleted style text<ul><li><paragraph>1.Sub Bulleted style text</paragraph></li></ul></li></ul><ul><li>Bulleted style text <strong>bold</strong><ul><li><paragraph>2.Sub Bulleted <strong>bold</strong></paragraph></li></ul></li></ul></some_tag>';
    protected $dom;
    public function processListsText( $loop = null ){
        $this->dom = new DomDocument('1.0', 'UTF-8');
        $this->dom->loadXML($this->xml_string);
        if(!$loop){
            //get all the li tags
            $li_set = $this->dom->getElementsByTagName('li');
        }
        else{
            $li_set = $loop;
        }
        foreach($li_set as $li){
            //check for child nodes
            if(! $li->hasChildNodes() ){
                continue;
            }
            foreach($li->childNodes as $child){
                if( $child->hasChildNodes() ){
                    //this li has children, maybe a <strong> tag
                    $this->processListsText( $child->childNodes );
                }
                if( ! ( $child instanceof DOMElement ) ){
                    continue;
                }
                if( ( $child->localName != 'paragraph') ||  ( $child instanceof DOMText )){
                    continue;
                }
                if( preg_match(self::AWKWARD_BULLET_REGEX, $child->textContent) == 0 ){
                    continue;
                }
                $clean_content = preg_replace(self::AWKWARD_BULLET_REGEX, '', $child->textContent);
                //set node to empty
                $child->nodeValue = '';
                //add updated content to node
                $child->appendChild($child->ownerDocument->createTextNode($clean_content));
                //$xml_output = $child->parentNode->ownerDocument->saveXML($child);
                //var_dump($xml_output);
            }
        }
    }
}
$importer = new MyDocumentImporter();
$importer->processListsText();

我可以看到的问题是，$child->textContent返回节点的纯文本内容，并剥离额外的子标记。所以:

<paragraph>2.Sub Bulleted <strong>bold</strong></paragraph>

是

<paragraph>Sub Bulleted bold</paragraph>

不再使用<strong>标签。

我有点难住了…任何人都可以看到一种方法来剥离不需要的字符，并保留"内部子"<strong>标签?

标签不一定总是<strong>，也可以是超链接<a href="#">，或<emphasize>。