details.xsl

<xsl:variable name="identifier"><xsl:value-of select="field_identifier" /></xsl:variable>
<h1><xsl:value-of select="php:function('Restaurant::getRestaruantData', $identifier)" disable-output-escaping="yes"/></h1>

template.php

<?php
 public static function getRestaurantData($identifier)
  {
    
    // get data from API
    $json_data = "https://mydatasource.com/api/data=".$identifier;
    
    $data = json_decode($json_data);
    
    foreach ($data as $item)
    {
      $html .= '<div class="rating">'.$item->rating.'</div>';
      $html .= '<div class="reviews>'.$item->reviews.'</div>';
    }
    
    return $html;
 
  }
?>