diff --git a/wire/config.php b/wire/config.php
index 6973b4b1..f4fb9e9d 100644
--- a/wire/config.php
+++ b/wire/config.php
@@ -46,28 +46,40 @@ if(!defined("PROCESSWIRE")) die();
  * always have this disabled for live/production sites since it reveals more information
  * than is advisible for security. 
  * 
- * You may also set this to the constant `Config::debugVerbose` to enable verbose debug mode,
- * which uses more memory and time. 
+ * You may also set this to one of the constants:
+ * - `Config::debugVerbose` (or int `2`) for verbose debug mode, which uses more memory/time. 
+ * - `Config::debugDev` (or string `dev`) for core development debug mode, which makes it use
+ *    newer JS libraries in some cases when we are testing them. 
  * 
  * #notes This enables debug mode for ALL requests. See the debugIf option for an alternative.
  * 
- * @var bool
+ * @var bool|string|int 
  *
  */
 $config->debug = false;
 
 /**
  * Enable debug mode if condition is met
+ * 
+ * ~~~~~
+ * $config->debug = false; // setting this to false required when using debugIf
+ * $config->debugIf = '123.123.123.123'; // true if user matches this IP address
+ * $config->debugIf = [ '123.123.123.123', '456.456.456.456' ]; // array of IPs (3.0.212)+
+ * $config->debugIf = 'function_name_to_call'; // callable function name
+ * $config->debugIf = function() { // callable function (3.0.212+)
+ *   return $_SERVER['SERVER_PORT'] === '8888'; 
+ * }; 
+ * ~~~~~
  *
  * Set debug mode to be false above, and then specify any one of the following here:
- * 1) IP address of user required to enable debug mode;
- * 2) Your own callable function name (i.e. "debug_mode") in /site/config.php that returns
- * true or false for debug mode;
- * 3) PCRE regular expression to match IP address of user (must start and end with a "/"
- * slash). If IP address matches, then debug mode is enabled. Regular expression
- * example: /^123\.456\.789\./ would match all IP addresses that started with 123.456.789.
+ * - IP address of user required to enable debug mode;
+ * - Array of IP addresses where that debug mode should be enabled for (3.0.212+).
+ * - Your own callable function in /site/config.php that returns true or false for debug mode.
+ * - PCRE regular expression to match IP address of user (must start and end with a "/"
+ *   slash). If IP address matches, then debug mode is enabled. Regular expression
+ *   example: `/^123\.456\.789\./` would match all IP addresses that started with 123.456.789.
  * 
- * #notes When used, this overrides $config->debug, changing it at runtime automatically. 
+ * #notes When used, this will override a false $config->debug, changing it at runtime automatically. 
  * @var string
  *
  */
diff --git a/wire/core/Config.php b/wire/core/Config.php
index 8cfabde3..1419d750 100644
--- a/wire/core/Config.php
+++ b/wire/core/Config.php
@@ -98,8 +98,8 @@
  * 
  * @property bool $advanced Special mode for ProcessWire system development. Not recommended for regular site development or production use. #pw-group-system
  * @property bool $demo Special mode for demonstration use that causes POST requests to be disabled. Applies to core, but may not be safe with 3rd party modules. #pw-group-system
- * @property bool|int $debug Special mode for use when debugging or developing a site. Recommended TRUE when site is in development and FALSE when not. Or set to Config::debugVerbose for verbose debug mode. #pw-group-system
- * @property string $debugIf Enable debug mode if condition is met #pw-group-system
+ * @property bool|int|string $debug Special mode for use when debugging or developing a site. Recommended TRUE when site is in development and FALSE when not. Or set to `Config::debug*` constant. #pw-group-system
+ * @property string|callable|array $debugIf Enable debug mode if condition is met. One of IP address to match, regex to match IP, array of IPs to match, or callable function that returns true|false. #pw-group-system
  * @property array $debugTools Tools, and their order, to show in debug mode (admin) #pw-group-system
  * 
  * @property string $ignoreTemplateFileRegex Regular expression to ignore template files #pw-group-template-files
@@ -202,6 +202,12 @@ class Config extends WireData {
 	 */
 	const debugVerbose = 2;
 
+	/**
+	 * Constant for core development debug mode (makes it use newer JS libraries in some cases)
+	 * 
+	 */
+	const debugDev = 'dev';
+
 	/**
 	 * Get config property
 	 *