xml to xml using xslt and php

I have a simple question about editing and (re)saving an xml document online. I noticed the example of how to do so on w3schools.com and it seemed pretty straight forward. However the example ONLY covers xml documents that have the same child tag names

Here's the example xml w3schools uses:

 <tool>
   <field id="prodName">
     <value>HAMMER HG2606</value>
   </field>
   <field id="prodNo">
     <value>32456240</value>
   </field>
   <field id="price">
     <value>$30.00</value>
   </field>
 </tool>

Updating the xml in the example works because each <field> has the same child tag name <value>. (The php function in control of the change:

function updateFile($xml)
 {
$xmlLoad = simplexml_load_file($xml);
$postKeys = array_keys($_POST);

foreach($xmlLoad->children() as $x)
{
  foreach($_POST as $key=>$value)
  {
    if($key == $x->attributes())
    {
      $x->value = $value; (((<---because all of child are called value each entry updates)))
    }
  }
}

the xslt loops through the tags by attribute:

<table border="0">
     <xsl:for-each select="tool/field">
     <tr>
       <td><xsl:value-of select="@id"/></td>
       <td>
       <input type="text">
       <xsl:attribute name="id">
         <xsl:value-of select="@id" />
       </xsl:attribute>
       <xsl:attribute name="name">
         <xsl:value-of select="@id" />
       </xsl:attribute>
       <xsl:attribute name="value">
         <xsl:value-of select="value" />
       </xsl:attribute>
       </input>
       </td>
     </tr>
     </xsl:for-each>
   </table>

my question is how can this work with more than one child tag 2 levels beep?

here's an example of the type of xml structure I mean:
<?xml version="1.0"?>
<EMPLOYMENT_OPPORTUNITIES>
       <OPPORTUNITY id="0">
               <INDEXABLE>0</INDEXABLE>
               <POSITION>Job1</POSITION>
               <DATELINE>03/17/2014</DATELINE>
               <LOCATION>files/examplefile.pdf</LOCATION>
      </OPPORTUNITY>
      <OPPORTUNITY id="1">
               <INDEXABLE>0</INDEXABLE>
               <POSITION>Job2</POSITION>
               <DATELINE>03/17/2014</DATELINE>
                <LOCATION>files/examplefile.pdf</LOCATION>
        </OPPORTUNITY>
</EMPLOYMENT_OPPORTUNITIES>


All of the w3school code in my example can be found here:

http://www.w3schools.com/xsl/xsl_editxml.asp

Thank you...