Update trait docs for PHP-8.2 (#1995)

The docs for traits probably need a good overhaul, but this documents the new constant in traits feature.

Author: Girgias

language/oop5/traits.xml

@@ -466,8 +466,8 @@ $example->x;
    </example>
    <para>
     If a trait defines a property then a class can not define a property with
-    the same name unless it is compatible (same visibility and initial value),
-    otherwise a fatal error is issued.
+    the same name unless it is compatible (same visibility and type,
+    readonly modifier, and initial value), otherwise a fatal error is issued.
    </para>
    <example xml:id="language.oop5.traits.properties.conflicts">
     <title>Conflict Resolution</title>
@@ -476,20 +476,74 @@ $example->x;
 <?php
 trait PropertiesTrait {
     public $same = true;
-    public $different = false;
+    public $different1 = false;
+    public bool $different2;
+    readonly public bool $different3;
 }
 
 class PropertiesExample {
     use PropertiesTrait;
     public $same = true;
-    public $different = true; // Fatal error
+    public $different1 = true; // Fatal error
+    public string $different2; // Fatal error
+    readonly public bool $different3; // Fatal error
 }
 ?>
 ]]>
     </programlisting>
    </example>
   </sect2>
 
+ <sect2 xml:id="language.oop5.traits.constants">
+  <title>&Constants;</title>
+  <para>
+   Traits can, as of PHP 8.2.0, also define constants.
+  </para>
+  <example xml:id="language.oop5.traits.constants.example">
+   <title>Defining Constants</title>
+   <programlisting role="php">
+<![CDATA[
+<?php
+trait ConstantsTrait {
+    public const FLAG_MUTABLE = 1;
+    final public const FLAG_IMMUTABLE = 5;
+}
+
+class ConstantsExample {
+    use ConstantTrait;
+}
+
+$example = new ConstantExample;
+$example::FLAG;
+?>
+]]>
+   </programlisting>
+  </example>
+  <para>
+   If a trait defines a constants then a class can not define a constants with
+   the same name unless it is compatible (same visibility, initial value, and
+   finality), otherwise a fatal error is issued.
+  </para>
+  <example xml:id="language.oop5.traits.constants.conflicts">
+   <title>Conflict Resolution</title>
+   <programlisting role="php">
+<![CDATA[
+<?php
+trait ConstantsTrait {
+    public const FLAG_MUTABLE = 1;
+    final public const FLAG_IMMUTABLE = 5;
+}
+
+class ConstantsExample {
+    use ConstantTrait;
+    public const FLAG_IMMUTABLE = 5; // Fatal error
+}
+?>
+]]>
+   </programlisting>
+  </example>
+ </sect2>
+
  </sect1>
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