Support rendering intersection types

As of PHP 8.1.0, intersection types are supported, so we already
prepare PhD for rendering respective types.  Since for now only pure
union and intersection types are supported, we don't handle complex
cases, although these are allowed by our DocBook DTD.

Closes GH-47.

Author: cmb69

phpdotnet/phd/Package/PHP/XHTML.php

@@ -155,9 +155,12 @@ abstract class Package_PHP_XHTML extends Package_Generic_XHTML {
         "refsynopsisdiv"               => null,
     );
 
-    /** @var int|null Number of already formatted types in the current union type */
+    /** @var int|null Number of already formatted types in the current compound type */
     private $num_types = null;
 
+    /** @var string|null The character to separate the current compound type, i.e. "|" or "&" */
+    private $type_separator = null;
+
     protected $pihandlers = array(
         'dbhtml'        => 'PI_DBHTMLHandler',
         'dbtimestamp'   => 'PI_DBHTMLHandler',
@@ -315,14 +318,16 @@ public function format_type($open, $tag, $attrs, $props) {
         if ($open) {
             if (isset($attrs[Reader::XMLNS_DOCBOOK]["class"])) {
                 $this->num_types = 0;
+                $this->type_separator = $attrs[Reader::XMLNS_DOCBOOK]["class"] === "union" ? "|" : "&";
             } elseif (isset($this->num_types)) {
-                if ($this->num_types > 0) $retval .= '|';
+                if ($this->num_types > 0) $retval .= $this->type_separator;
                 $this->num_types++;
             }
             $retval .= '<span class="type">';
         } else {
             if (isset($attrs[Reader::XMLNS_DOCBOOK]["class"])) {
                 $this->num_types = null;
+                $this->type_separator = null;
             }
             $retval .= '</span>';
         }
@@ -443,7 +448,7 @@ public function format_methodsynopsis($open, $name, $attrs, $props) {
                 }
                 $types[] = '<span class="type">' . $formatted_type . '</span>';
             }
-            $type = implode('|', $types);
+            $type = implode($this->type_separator, $types);
             if (count($types) > 1) {
                 $type = '<span class="type">' . $type . '</span>';
             }