diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
index f2ea023803..f9ca187953 100644
--- a/.php-cs-fixer.php
+++ b/.php-cs-fixer.php
@@ -13,6 +13,7 @@
 
 $config->setRules([
     'array_indentation' => true,
+    'constant_case' => true,
     'indentation_type' => true,
     'line_ending' => true,
     'no_extra_blank_lines' => true,
diff --git a/cal.php b/cal.php
index 55599eb7e0..990040cf5e 100644
--- a/cal.php
+++ b/cal.php
@@ -18,7 +18,7 @@
  a fallback to display the actual month/year.
 */
 
-$begun = FALSE; $errors = array();
+$begun = false; $errors = array();
 $id = isset($_GET['id']) ? (int) $_GET['id'] : 0;
 $cy = isset($_GET['cy']) ? (int) $_GET['cy'] : 0;
 $cm = isset($_GET['cm']) ? (int) $_GET['cm'] : 0;
@@ -37,7 +37,7 @@
     if ($event = load_event($id)) {
         site_header("Event: " . stripslashes(htmlentities($event['sdesc'], ENT_QUOTES | ENT_IGNORE, 'UTF-8')), $site_header_config);
         display_event($event, 0);
-        $begun = TRUE;
+        $begun = true;
     }
     // Unable to find event, put this to the error messages' list
     else {
@@ -63,7 +63,7 @@
                 display_event($event, 0);
                 echo "<br>";
             }
-            $begun = TRUE;
+            $begun = true;
         }
 
         // Unable to load events for that day
@@ -110,10 +110,10 @@
 }
 
 // Get events list for a whole month
-$events = load_events($date, TRUE);
+$events = load_events($date, true);
 
 // If there was an error, or there are no events, this is an error
-if ($events === FALSE || count($events) == 0) {
+if ($events === false || count($events) == 0) {
     $errors[] = "No events found for this month";
 }
 
@@ -257,7 +257,7 @@ function load_event($id)
 {
     // Open events CSV file, return on error
     $fp = @fopen("backend/events.csv",'r');
-    if (!$fp) { return FALSE; }
+    if (!$fp) { return false; }
 
     // Read as we can, event by event
     while (!feof($fp)) {
@@ -266,7 +266,7 @@ function load_event($id)
 
       // Return with the event, if it's ID is the one
       // we search for (also close the file)
-      if ($event !== FALSE && $event['id'] == $id) {
+      if ($event !== false && $event['id'] == $id) {
         fclose($fp);
         return $event;
       }
@@ -274,12 +274,12 @@ function load_event($id)
 
     // Close file, and return sign of failure
     fclose($fp);
-    return FALSE;
+    return false;
 }
 
 // Load a list of events. Either for a particular day ($from) or a whole
 // month (if second parameter specified with TRUE)
-function load_events($from, $whole_month = FALSE)
+function load_events($from, $whole_month = false)
 {
     // Take advantage of the equality behavior of this date format
     $from_date = date("Y-m-d", $from);
@@ -292,14 +292,14 @@ function load_events($from, $whole_month = FALSE)
 
     // Try to open the events file for reading, return if unable to
     $fp = @fopen("backend/events.csv",'r');
-    if (!$fp) { return FALSE; }
+    if (!$fp) { return false; }
 
     // For all events, read in the event and check it if fits our scope
     while (!feof($fp)) {
 
         // Read the event data into $event, or continue with next
         // line, if there was an error with this line
-        if (($event = read_event($fp)) === FALSE) {
+        if (($event = read_event($fp)) === false) {
             continue;
         }
 
@@ -345,12 +345,12 @@ function load_events($from, $whole_month = FALSE)
 function read_event($fp)
 {
     // We were unable to read a line from the file, return
-    if (($linearr = fgetcsv($fp, 8192)) === FALSE) {
-        return FALSE;
+    if (($linearr = fgetcsv($fp, 8192)) === false) {
+        return false;
     }
 
     // Corrupt line in CSV file
-    if (count($linearr) < 13) { return FALSE; }
+    if (count($linearr) < 13) { return false; }
 
     // Get components
     list(
@@ -386,11 +386,11 @@ function valid_year($year)
 
     // We only allow this and the next year for displays
     if ($year != $current_year && $year != $current_year+1) {
-        return FALSE;
+        return false;
     }
 
     // The year is all right
-    return TRUE;
+    return true;
 }
 
 ?>
diff --git a/download-docs.php b/download-docs.php
index bdd5d4a247..471f153049 100644
--- a/download-docs.php
+++ b/download-docs.php
@@ -118,7 +118,7 @@
             $changed = @filemtime($filepath);
 
             // Size available, collect information
-            if ($size !== FALSE) {
+            if ($size !== false) {
                 $files[$langcode][$formatname] = array(
                     $link_to,
                     (int) ($size/1024),
@@ -170,8 +170,8 @@
     foreach ($files as $langcode => $lang_files) {
 
         // See if current language is the preferred one
-        if ($langcode == $LANG) { $preflang = TRUE; }
-        else { $preflang = FALSE; }
+        if ($langcode == $LANG) { $preflang = true; }
+        else { $preflang = false; }
 
         // Highlight manual in preferred language
         if ($preflang) {
diff --git a/download-logos.php b/download-logos.php
index 85f59dd1c4..b331754d91 100644
--- a/download-logos.php
+++ b/download-logos.php
@@ -65,7 +65,7 @@ function random_bgcolor($min, $max): void
 </p>
 
 <div class="center logo-list">
-  <?php print_image("logos/new-php-logo.svg", "PHP logo", FALSE, 'width="200"'); ?>
+  <?php print_image("logos/new-php-logo.svg", "PHP logo", false, 'width="200"'); ?>
   <br>
   <a href="/images/logos/new-php-logo.svg">SVG</a> |
   <a href="/images/logos/new-php-logo.png">PNG</a>
@@ -78,7 +78,7 @@ function random_bgcolor($min, $max): void
 </p>
 
 <div class="center logo-list">
-  <?php print_image("logos/php-logo.svg", "PHP logo", FALSE, 'width="200"'); ?>
+  <?php print_image("logos/php-logo.svg", "PHP logo", false, 'width="200"'); ?>
   <br>
   <a href="/images/logos/php-logo.svg">SVG</a> |
   <a href="/images/logos/php-logo-bigger.png">PNG</a>
diff --git a/mailing-lists.php b/mailing-lists.php
index 36186c820b..37993fd764 100644
--- a/mailing-lists.php
+++ b/mailing-lists.php
@@ -189,50 +189,50 @@
       array (
           'php-announce', 'Announcements',
           'Announcements of new PHP releases are sent to this very low-volume list',
-          TRUE, FALSE, FALSE, "php.announce"
+          true, false, false, "php.announce"
       ),
       array (
           'php-general', 'General user list',
           'This is a high volume list for general PHP support; ask PHP questions here',
-          FALSE, TRUE, TRUE, "php.general"
+          false, true, true, "php.general"
       ),
       array (
           'php-windows', 'Windows PHP users list',
           'Using PHP on Microsoft Windows',
-          FALSE, TRUE, TRUE, "php.windows"
+          false, true, true, "php.windows"
       ),
 
       'Subject specific lists for PHP users',
       array (
           'php-install', 'Installation issues and problems',
           'How to install PHP with particular configurations and servers',
-          FALSE, TRUE, TRUE, "php.install"
+          false, true, true, "php.install"
       ),
       array (
           'php-db', 'Databases and PHP',
           'This list is for the discussion of PHP database topics',
-          FALSE, TRUE, TRUE, "php.db"
+          false, true, true, "php.db"
       ),
       array (
           'php-i18n', 'Unicode and Internationalization',
           'Unicode support, Internationalization (i18n) and localization (l10n) issues and features',
-          FALSE, TRUE, TRUE, "php.i18n"
+          false, true, true, "php.i18n"
       ),
       array (
           'php-evangelism', 'PHP evangelism mailing list',
           'A list for people interested in promoting PHP and learning good reasons to support PHP in the enterprise',
-          TRUE, TRUE, TRUE, "php.evangelism"
+          true, true, true, "php.evangelism"
       ),
       array (
           'soap', 'PHP SOAP list',
           'List for the SOAP developers',
-          FALSE, FALSE, FALSE, 'php.soap'
+          false, false, false, 'php.soap'
       ),
       'Non-English language mailing lists',
       array (
           'php-es', 'Spanish PHP Mailing list',
           'List for Spanish speaking people interested in PHP',
-          FALSE, FALSE, FALSE, 'php.general.es'
+          false, false, false, 'php.general.es'
       ),
 
   );
@@ -244,37 +244,37 @@
       array (
           'internals', 'Internals list',
           'A medium volume list for those who want to help out with the development of PHP',
-          FALSE, 'php-internals', TRUE, "php.internals"
+          false, 'php-internals', true, "php.internals"
       ),
       array (
           'internals-win', 'Windows Internals list',
           'A low volume list for those who want to help out with the development of PHP on Windows',
-          FALSE, FALSE, TRUE, "php.internals.win"
+          false, false, true, "php.internals.win"
       ),
       array (
           'php-cvs', 'Git commit list',
           'All commits to internals (php-src) and the Zend Engine are posted to this list automatically',
-          TRUE, TRUE, FALSE, "php.cvs"
+          true, true, false, "php.cvs"
       ),
       array (
           'git-pulls', 'Git pull requests',
           'Pull requests from Github',
-          FALSE, FALSE, FALSE, "php.git-pulls"
+          false, false, false, "php.git-pulls"
       ),
       array (
           'php-qa', 'Quality Assurance list',
           'List for the members of the PHP-QA Team',
-          FALSE, TRUE, FALSE, "php.qa"
+          false, true, false, "php.qa"
       ),
       array (
           'php-bugs', 'General bugs',
           'General bug activity are posted here',
-          FALSE, FALSE, FALSE, "php.bugs"
+          false, false, false, "php.bugs"
       ),
       array (
           'standards', 'PHP Standardization and interoperability list',
           'Development of language standards',
-          FALSE, FALSE, FALSE, "php.standards"
+          false, false, false, "php.standards"
       ),
 
       'PHP internal website mailing lists',
@@ -282,24 +282,24 @@
           'php-webmaster', 'PHP php.net internal infrastructure discussion',
           'List for discussing and maintaining the php.net web infrastructure.<br>
        For general PHP support questions, see "General Mailing Lists" or the <a href="/support.php">support page</a>',
-          FALSE, FALSE, FALSE, "php.webmaster"
+          false, false, false, "php.webmaster"
       ),
 
       'PHP documentation mailing lists',
       array (
           'phpdoc', 'Documentation discussion',
           'List for discussing the PHP documentation',
-          FALSE, TRUE, FALSE, "php.doc"
+          false, true, false, "php.doc"
       ),
       array (
           'doc-cvs', 'Documentation changes and commits',
           'Changes to the documentation are posted here',
-          TRUE, "php-doc-cvs", FALSE, "php.doc.cvs"
+          true, "php-doc-cvs", false, "php.doc.cvs"
       ),
       array (
           'doc-bugs', 'Documentation bugs',
           'Documentation bug activity (translations, sources, and build system) are posted here',
-          TRUE, 'php-doc-bugs', FALSE, "php.doc.bugs"
+          true, 'php-doc-bugs', false, "php.doc.bugs"
       ),
   );
 
@@ -319,9 +319,9 @@ function output_lists_table($mailing_lists): void
             // Let the list name defined with a string, if the
             // list is archived under a different name then php.net
             // uses for it (for backward compatibilty for example)
-            if ($listinfo[4] !== FALSE) {
-                $larchive = ($listinfo[4] === TRUE ? $listinfo[0] : $listinfo[4]);
-            } else { $larchive = FALSE; }
+            if ($listinfo[4] !== false) {
+                $larchive = ($listinfo[4] === true ? $listinfo[0] : $listinfo[4]);
+            } else { $larchive = false; }
             echo '<td>' . ($larchive ? "<a href=\"http://marc.info/?l={$larchive}\">yes</a>" : 'n/a') . '</td>';
             echo '<td>' . ($listinfo[6] ? "<a href=\"news://news.php.net/{$listinfo[6]}\">yes</a> <a href=\"http://news.php.net/group.php?group={$listinfo[6]}\">http</a>" : 'n/a') . '</td>';
             echo '<td><input name="maillist" type="radio" value="' . $listinfo[0] . '"></td>';
diff --git a/manual/add-note.php b/manual/add-note.php
index 107d4c3a72..7db4a4e4b2 100644
--- a/manual/add-note.php
+++ b/manual/add-note.php
@@ -18,11 +18,11 @@
 }
 
 // Decide on whether all vars are present for processing
-$process = TRUE;
+$process = true;
 $needed_vars = array('note', 'user', 'sect', 'redirect', 'action', 'func', 'arga', 'argb', 'answer');
 foreach ($needed_vars as $varname) {
     if (empty($_POST[$varname])) {
-        $process = FALSE;
+        $process = false;
         break;
     }
 }
@@ -45,7 +45,7 @@
     }
 
     // We don't know of any error now
-    $error = FALSE;
+    $error = false;
 
     // No note specified
     if (strlen($note) == 0) {
@@ -104,15 +104,15 @@
 
         // If there is any non-header result, then it is an error
         if ($result) {
-            if (strpos($result, '[TOO MANY NOTES]') !== FALSE) {
+            if (strpos($result, '[TOO MANY NOTES]') !== false) {
                 print "<p class=\"formerror\">As a security precaution, we only allow a certain number of notes to be submitted per minute. At this time, this number has been exceeded. Please re-submit your note in about a minute.</p>";
-            } elseif (($pos = strpos($result, '[SPAMMER]')) !== FALSE) {
+            } elseif (($pos = strpos($result, '[SPAMMER]')) !== false) {
                 $ip       = trim(substr($result, $pos+9));
                 $spam_url = $ip_spam_lookup_url . $ip;
                 print '<p class="formerror">Your IP is listed in one of the spammers lists we use, which aren\'t controlled by us. More information is available at <a href="'.$spam_url.'">'.$spam_url.'</a>.</p>';
-            } elseif (strpos($result, '[SPAM WORD]') !== FALSE) {
+            } elseif (strpos($result, '[SPAM WORD]') !== false) {
                 echo '<p class="formerror">Your note contains a prohibited (usually SPAM) word. Please remove it and try again.</p>';
-            } elseif (strpos($result, '[CLOSED]') !== FALSE) {
+            } elseif (strpos($result, '[CLOSED]') !== false) {
                 echo '<p class="formerror">Due to some technical problems this service isn\'t currently working. Please try again later. Sorry for any inconvenience.</p>';
             } else {
                 echo "<!-- $result -->";
@@ -140,7 +140,7 @@
     // Print out preview of note
     echo '<p>This is what your entry will look like, roughly:</p>';
     echo '<div id="usernotes">';
-    manual_note_display(time(), $user, $note, FALSE);
+    manual_note_display(time(), $user, $note, false);
     echo '</div><br><br>';
 }
 
diff --git a/mirror.php b/mirror.php
index c153bc01ef..1df2a16826 100644
--- a/mirror.php
+++ b/mirror.php
@@ -31,8 +31,8 @@
             $MIRROR_IMAGE = make_image(
                 'mirror.' . $ext,
                 htmlspecialchars(mirror_provider()),
-                FALSE,
-                FALSE,
+                false,
+                false,
                 'backend'
             );
 
diff --git a/quickref.php b/quickref.php
index cb4c757de6..6e33915c99 100644
--- a/quickref.php
+++ b/quickref.php
@@ -54,7 +54,7 @@ function quickref_table($functions, $sort = true): void
 $p = 0;
 
 // Get all file names from the directory
-while (($entry = readdir($dirh)) !== FALSE) {
+while (($entry = readdir($dirh)) !== false) {
 
     // Skip names starting with a dot
     if (substr($entry, 0, 1) == ".") { continue; }
@@ -70,7 +70,7 @@ function quickref_table($functions, $sort = true): void
 
             // If $notfound is a substring of $funcname then overwrite the score
             // similar_text() gave it.
-            if ($p < 70 && ($pos = strpos($funcname, $notfound)) !== FALSE) {
+            if ($p < 70 && ($pos = strpos($funcname, $notfound)) !== false) {
                 $p = 90 - $pos;
             }
             $temp[$entry] = $p;
@@ -93,7 +93,7 @@ function quickref_table($functions, $sort = true): void
 
         // If the two are more then 70% similar or $notfound is a substring
         // of $funcname, then the match is a very similar one
-        if ($p >= 70 || (strpos($functions[$file], $notfound) !== FALSE)) {
+        if ($p >= 70 || (strpos($functions[$file], $notfound) !== false)) {
             $maybe[$file] = '<b>' . $functions[$file] . '</b>';
         }
         // Otherwise it is just similar