print('<pre>');
print_r( @get_defined_constants() );
print('</pre>');

To be sure, that only logged in user can see the list, I will add an additional query to check if the user is logged in.

if ( is_user_logged_in() ) {
	print('<pre>');
	print_r( @get_defined_constants() );
	print('</pre>');
}

The output can also be checked by user rights with if ( current_user_can('manage_options') ) {. You can read more about it in a previous article or an article with examples for use the rights.

As an alternativ, the Plugins WP System Health and Debug Objects can be very helpful, which lists all constants.
Have fun!

fetch_feed() Since WordPress 2.8

With version 2.8 of WordPress, they add the class SimplePie into the core. SimplePie has always distinguished by a very rapid development and a stable user-friendly class. Before MagpieRSS has been used, which in many cases was not available and the development is rather slow. For some time SimplePie is no longer be maintained by the developer, which worried the developer community. But developers from the WordPress team took care of it and keep the class alive. More information can be find on the blog WP Dev Updates

Now the class is in the core of WordPress and is capable of generating RSS and ATOM feeds. It uses the cache of WordPress and can be controlled via a hook.

But first a small sample to read a feed with the class in WordPress.

<?php
include_once(ABSPATH . WPINC . '/feed.php');
$rss = fetch_feed('http://bueltge.de/feed/');
$rss_items = $rss->get_items( 0, $rss->get_item_quantity(5) );
if ( !$rss_items ) {
    echo 'no items';
} else {
    foreach ( $rss_items as $item ) {
        echo '<p><a href="' . $item->get_permalink() . '">' . $item->get_title() . '</a></p>';
    }
}
?>

The small sample reads my feed and returns the last 5 entries.

Essential is the function fetch_feed(). This function has a hook which can make influence on caching - wp_feed_cache_transient_lifetime.
The standard of the cache is set to 12 hours ( 43,200 ), which is not always the favorite setting for users. The value is operated on the method WP_Feed_Cache_Transient(), parameter $lifetime. Therefore, it is advisable to use the following little query, be it in the Plugin or in the functions.php of the theme.

add_filter( 'wp_feed_cache_transient_lifetime', create_function( '$a', 'return 1800;' ) );

In this example, I set the cache to 30 minutes. With the help of Conditional Tags you can control the whole of it so that the cache-hook is only activated when you click on a page (is_page()) or for example you are in the front end (!is_admin()) of the blog. Here you must simply use the opportunities and adapt to your own needs.

A small possibility I would like to point out more, available as of WordPress 2.9 (ticket 11117), to simplify debugging for developers. Thus, the cache is disabled in the environment, if the constant WP_DEBUG is set, which can be important now and then. Setting the constant is usually done in the wp-config.php of the installation, or as alternative in the Plugin.

function do_not_cache_feeds(&$feed) {
	$feed->enable_cache(false);
}

if ( defined('WP_DEBUG') && WP_DEBUG )
	add_action( 'wp_feed_options', 'do_not_cache_feeds' );

fetch_rss()

Another function is fetch_rss(), which was set with WordPress 2.8 on the suspense list. As an alternative, the above function is active. Current is fetch_rss() still available and is also supported. Therefore, for completeness, also the possibility to influence the cache.

Here an example to read feed and output the last 5 entries of the feed

<?php
include_once(ABSPATH . WPINC . '/rss.php');
$rss = fetch_rss('http://bueltge.de/feed/');
$rss_items = array_slice($rss->items, 0, 5);
if ( empty($rss_items) ) {
    echo 'no items';
} else {
    foreach ( $rss_items as $item ) {
        echo '<p><a href="' . $item['link'] . '">' . $item['title'] . '</a></p>';
    }
}
?>

Here, the function fetch_rss() is used for reading and the cache can be changed via the constants. This must defined either directly in wp-config.php where they will apply globally to all applications, or you need to integrate them into its own functions.

define('MAGPIE_CACHE_ON', 0); // deactivate cache
define('MAGPIE_CACHE_AGE', 60*60) // Cache 1 hour in seconds

Conclusion

Since WordPress decided not to support MagpieRSS any longer in the future, you should only deal with SimplePie and not with the second possibility.

... which you can activate with the help of a constant; stored in wp-config.php, you have access to the script.

define('WP_ALLOW_REPAIR', true);

Call the script from the outside at the following address ...
http://example.com/wp-admin/maint/repair.php

... where you either repair the database or run the optimization. Technically, there is no magic behind this work, but the familiar SQL statements ANALYZE TABLE, REPAIR TABLE and OPTIMIZE TABLE.

I guess that will start a debate, why with the constant and why from the outside, etc. - leave your comment here. Alternatively, anyone can contribute to WordPress and discuss directly with the developers or enter changes directly to the code.

Users of Gmail are aware of the possibility in a web application: you move content into the trash and the content will be deleted after a certain time. Alternatively, you can also restore the content, always depending on a defined time frame.

WordPress integrates this function also in WordPress 2.9 for articles and comments. Some screenshots showing the function in articles and comments.

The time period is via constant defined, default are 30 days. If you want to change this value, it must be defined in wp-config.php.
define( 'EMPTY_TRASH_DAYS', 30 );

For developers, there are two hooks - for articles and comments, where you can intervene.

* @uses do_action() on 'untrash_post' before undeletion
* @uses do_action() on 'untrashed_post' after undeletion


* @uses do_action() on 'untrash_comment' before undeletion
* @uses do_action() on 'untrashed_comment' after undeletion


Otherwise, version 2.9 gets some more advanced features for media, as the users in the last survey decided. These will also be available in the core and thus the system continues to inflate. A pity, in my view that the user does not use the option of "Canonical Plugins" .

Until WordPress 2.7

Up to this version of WordPress it works only with an adjustment in the core, in wp-includes/class-snoopy.php. Here you have to change the settings of $proxy_host, $proxy_port and $_isproxy. The value of var $_isproxy = false; will of course have TRUE as value.

var $host       = "www.php.net"; // host name we are connecting to
var $port       = 8080; // port we are connecting to
var $proxy_host = ""; // proxy host to use
var $proxy_port = ""; // proxy port to use
var $proxy_user = ""; // proxy user to use
var $proxy_pass = ""; // proxy password to use
var $_isproxy   = true; // set if using a proxy server

WordPress 2.8

With the new version it is much easier, because no more intrusion into the core files is necessary and the possibility to define the values in the configuration file wp-config.php.

define('WP_PROXY_HOST', '192.168.84.101');
define('WP_PROXY_PORT', '8080');
define('WP_PROXY_USERNAME', 'my_user_name');
define('WP_PROXY_PASSWORD', 'my_password');
define('WP_PROXY_BYPASS_HOSTS', 'localhost, www.example.com');

Various references are also inTicket 4011.

<?php
define('DIR_ROOT', 'http://example.com');
define('DIR_STYLESHEETS', DIR_ROOT . '/css');
define('DIR_IMAGES', DIR_ROOT . '/images');
define('DIR_JAVASCRIPT', DIR_ROOT . '/js');
?>

In your theme you use the constants like this:

<script src="<?php echo DIR_JAVASCRIPT; ?>/myeffects.js" type="text/javascript"></script>
<img src="<?php echo DIR_IMAGES; ?>/myimage.jpg" alt="foo" />

Easy, right? Mostly a little stylesheet is enough for special WordPress adjustments, which you load after the stylesheets of the CMS.

Just a few lines of code are enough and you can work with the „new“ constants.

// Pre-2.6 compatibility
if ( !defined( 'WP_CONTENT_URL' ) )
	define( 'WP_CONTENT_URL', get_option( 'siteurl' ) . '/wp-content' );
if ( !defined( 'WP_CONTENT_DIR' ) )
	define( 'WP_CONTENT_DIR', ABSPATH . 'wp-content' );
if ( !defined( 'WP_PLUGIN_URL' ) )
	define( 'WP_PLUGIN_URL', WP_CONTENT_URL. '/plugins' );
if ( !defined( 'WP_PLUGIN_DIR' ) )
	define( 'WP_PLUGIN_DIR', WP_CONTENT_DIR . '/plugins' );
if ( !defined( 'WP_LANG_DIR') )
	define( 'WP_LANG_DIR', WP_CONTENT_DIR . '/languages' );

I use this solution quite a long time. You can find the solution in the WordPress Codex now - „Determining Plugin and Content Directories“.