diff --git a/language/control-structures/for.xml b/language/control-structures/for.xml
index b3fe2b350578..9862411e3f02 100644
--- a/language/control-structures/for.xml
+++ b/language/control-structures/for.xml
@@ -142,97 +142,61 @@ endfor;
   </informalexample>
  </para>
  <simpara>
-  It's common for many users to iterate through arrays like in the
-  example below.
+  Expressions <varname>expr2</varname> and <varname>expr3</varname> are
+  evaluated every iteration. It's advisable to use simple expressions in these
+  places to avoid performance issues. For example, if the number of iterations
+  is known in advance, it is better to use a variable instead of a function call
+  in <varname>expr2</varname>:
  </simpara>
  <para>
   <informalexample>
-   <programlisting role="php">
+   <programlisting role="php" annotations="non-interactive">
 <![CDATA[
 <?php
-/*
- * This is an array with some data we want to modify
- * when running through the for loop.
- */
-$people = array(
-    array('name' => 'Kalle', 'salt' => 856412),
-    array('name' => 'Pierre', 'salt' => 215863)
-);
 
-for($i = 0; $i < count($people); ++$i) {
-    $people[$i]['salt'] = random_int(100000, 999999);
+$people = ['Kalle', 'Pierre'];
+
+// Bad practice: calling a function on every iteration
+for($i = 0; $i < getIterationCount($people); ++$i) {
+    $people[$i] .= ' is cool';
 }
-var_dump($people);
-]]>
-   </programlisting>
-   &example.outputs.similar;
-   <screen>
-<![CDATA[
-array(2) {
-  [0]=>
-  array(2) {
-    ["name"]=>
-    string(5) "Kalle"
-    ["salt"]=>
-    int(454478)
-  }
-  [1]=>
-  array(2) {
-    ["name"]=>
-    string(6) "Pierre"
-    ["salt"]=>
-    int(776978)
-  }
+
+// Good practice: storing the count in a variable
+for($i = 0, $peopleCount = getIterationCount($people); $i < $peopleCount; ++$i) {
+    $people[$i] .= ' is cool';
 }
+
 ]]>
-   </screen>
+   </programlisting>
   </informalexample>
  </para>
  <simpara>
-  The above code can be slow, because the array size is fetched on
-  every iteration. Since the size never changes, the loop can be easily
-  optimized by using an intermediate variable to store the size instead
-  of repeatedly calling <function>count</function>:
+  In the example above, the function is called on every iteration of the
+  first loop, even though it always returns the same value. Storing that
+  value in a variable, as the second loop does, calls the function once.
+  Note that the number of iterations is then fixed: if the array is
+  modified inside the loop, the stored value no longer reflects its size.
  </simpara>
- <para>
-  <informalexample>
-   <programlisting role="php">
-<![CDATA[
-<?php
-$people = array(
-    array('name' => 'Kalle', 'salt' => 856412),
-    array('name' => 'Pierre', 'salt' => 215863)
-);
 
-for($i = 0, $size = count($people); $i < $size; ++$i) {
-    $people[$i]['salt'] = random_int(100000, 999999);
-}
-var_dump($people);
-]]>
-   </programlisting>
-   &example.outputs.similar;
-   <screen>
-<![CDATA[
-array(2) {
-  [0]=>
-  array(2) {
-    ["name"]=>
-    string(5) "Kalle"
-    ["salt"]=>
-    int(454478)
-  }
-  [1]=>
-  array(2) {
-    ["name"]=>
-    string(6) "Pierre"
-    ["salt"]=>
-    int(776978)
-  }
-}
-]]>
-   </screen>
-  </informalexample>
- </para>
+ <note>
+  <simpara>
+   The size of an <type>array</type> is stored with the array, which means that
+   calling the built-in function <function>count</function> does not require
+   counting the elements and does not cause performance issues. This does not
+   apply to <constant>COUNT_RECURSIVE</constant>, which walks the whole array.
+   Care should also be taken when using <function>count</function> on objects
+   implementing <interfacename>Countable</interfacename>, as such calls can be
+   more expensive.
+  </simpara>
+ </note>
+
+ <note>
+  <simpara>
+   The <literal>for</literal> loop is not the recommended way to
+   iterate over arrays. The &foreach; loop is specifically
+   designed for this purpose and is usually more convenient.
+  </simpara>
+ </note>
 </sect1>
 
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