diff --git a/lib/Authentication.php b/lib/Authentication.php
index da247630..f9683940 100644
--- a/lib/Authentication.php
+++ b/lib/Authentication.php
@@ -1,6 +1,48 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Authentication module for RSS-Bridge.
+ *
+ * This class implements an authentication module for RSS-Bridge, utilizing the
+ * HTTP authentication capabilities of PHP.
+ *
+ * _Notice_: Authentication via HTTP does not prevent users from accessing files
+ * on your server. If your server supports `.htaccess`, you should globally restrict
+ * access to files instead.
+ *
+ * @link https://php.net/manual/en/features.http-auth.php HTTP authentication with PHP
+ * @link https://httpd.apache.org/docs/2.4/howto/htaccess.html Apache HTTP Server
+ * Tutorial: .htaccess files
+ *
+ * @todo This class should respond with an error when creating an object from it.
+ * See {@see Bridge}, {@see Cache} or {@see Format} for reference.
+ * @todo Configuration parameters should be stored internally instead of accessing
+ * the configuration class directly.
+ * @todo Add functions to detect if a user is authenticated or not. This can be
+ * utilized for limiting access to authorized users only.
+ */
 class Authentication {
 
+	/**
+	 * Requests the user for login credentials if necessary.
+	 *
+	 * Responds to an authentication request or returns the `WWW-Authenticate`
+	 * header if authentication is enabled in the configuration of RSS-Bridge
+	 * (`[authentication] enable = true`).
+	 *
+	 * @return void
+	 */
 	public static function showPromptIfNeeded() {
 
 		if(Configuration::getConfig('authentication', 'enable') === true) {
@@ -13,6 +55,13 @@ class Authentication {
 
 	}
 
+	/**
+	 * Verifies if an authentication request was received and compares the
+	 * provided username and password to the configuration of RSS-Bridge
+	 * (`[authentication] username` and `[authentication] password`).
+	 *
+	 * @return bool True if authentication succeeded.
+	 */
 	public static function verifyPrompt() {
 
 		if(isset($_SERVER['PHP_AUTH_USER']) && isset($_SERVER['PHP_AUTH_PW'])) {
diff --git a/lib/BridgeAbstract.php b/lib/BridgeAbstract.php
index aa654111..b02280e4 100644
--- a/lib/BridgeAbstract.php
+++ b/lib/BridgeAbstract.php
@@ -1,32 +1,112 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
 
+/**
+ * An abstract class for bridges
+ *
+ * This class implements {@see BridgeInterface} with most common functions in
+ * order to reduce code duplication. Bridges should inherit from this class
+ * instead of implementing the interface manually.
+ *
+ * @todo Move constants to the interface (this is supported by PHP)
+ * @todo Change visibility of constants to protected
+ * @todo Return `self` on more functions to allow chaining
+ * @todo Add specification for PARAMETERS ()
+ * @todo Add specification for $items
+ */
 abstract class BridgeAbstract implements BridgeInterface {
 
+	/**
+	 * Name of the bridge
+	 *
+	 * Use {@see BridgeAbstract::getName()} to read this parameter
+	 */
 	const NAME = 'Unnamed bridge';
-	const URI = '';
-	const DESCRIPTION = 'No description provided';
-	const MAINTAINER = 'No maintainer';
-	const CACHE_TIMEOUT = 3600;
-	const PARAMETERS = array();
-
-	protected $items = array();
-	protected $inputs = array();
-	protected $queriedContext = '';
 
 	/**
-	* Return items stored in the bridge
-	* @return mixed
-	*/
+	 * URI to the site the bridge is intended to be used for.
+	 *
+	 * Use {@see BridgeAbstract::getURI()} to read this parameter
+	 */
+	const URI = '';
+
+	/**
+	 * A brief description of what the bridge can do
+	 *
+	 * Use {@see BridgeAbstract::getDescription()} to read this parameter
+	 */
+	const DESCRIPTION = 'No description provided';
+
+	/**
+	 * The name of the maintainer. Multiple maintainers can be separated by comma
+	 *
+	 * Use {@see BridgeAbstract::getMaintainer()} to read this parameter
+	 */
+	const MAINTAINER = 'No maintainer';
+
+	/**
+	 * The default cache timeout for the bridge
+	 *
+	 * Use {@see BridgeAbstract::getCacheTimeout()} to read this parameter
+	 */
+	const CACHE_TIMEOUT = 3600;
+
+	/**
+	 * Parameters for the bridge
+	 *
+	 * Use {@see BridgeAbstract::getParameters()} to read this parameter
+	 */
+	const PARAMETERS = array();
+
+	/**
+	 * Holds the list of items collected by the bridge
+	 *
+	 * Items must be collected by {@see BridgeInterface::collectData()}
+	 *
+	 * Use {@see BridgeAbstract::getItems()} to access items.
+	 *
+	 * @var array
+	 */
+	protected $items = array();
+
+	/**
+	 * Holds the list of input parameters used by the bridge
+	 *
+	 * Do not access this parameter directly!
+	 * Use {@see BridgeAbstract::setInputs()} and {@see BridgeAbstract::getInput()} instead!
+	 *
+	 * @var array
+	 */
+	protected $inputs = array();
+
+	/**
+	 * Holds the name of the queried context
+	 *
+	 * @var string
+	 */
+	protected $queriedContext = '';
+
+	/** {@inheritdoc} */
 	public function getItems(){
 		return $this->items;
 	}
 
 	/**
-	 * Sets the input values for a given context. Existing values are
-	 * overwritten.
+	 * Sets the input values for a given context.
 	 *
 	 * @param array $inputs Associative array of inputs
-	 * @param string $context The context name
+	 * @param string $queriedContext The context name
+	 * @return void
 	 */
 	protected function setInputs(array $inputs, $queriedContext){
 		// Import and assign all inputs to their context
@@ -103,9 +183,15 @@ abstract class BridgeAbstract implements BridgeInterface {
 	}
 
 	/**
-	* Defined datas with parameters depending choose bridge
-	* @param array array with expected bridge paramters
-	*/
+	 * Set inputs for the bridge
+	 *
+	 * Returns errors and aborts execution if the provided input parameters are
+	 * invalid.
+	 *
+	 * @param array List of input parameters. Each element in this list must
+	 * relate to an item in {@see BridgeAbstract::PARAMETERS}
+	 * @return void
+	 */
 	public function setDatas(array $inputs){
 
 		if(empty(static::PARAMETERS)) {
@@ -148,7 +234,7 @@ abstract class BridgeAbstract implements BridgeInterface {
 	 * Returns the value for the provided input
 	 *
 	 * @param string $input The input name
-	 * @return mixed Returns the input value or null if the input is not defined
+	 * @return mixed|null The input value or null if the input is not defined
 	 */
 	protected function getInput($input){
 		if(!isset($this->inputs[$this->queriedContext][$input]['value'])) {
@@ -157,30 +243,37 @@ abstract class BridgeAbstract implements BridgeInterface {
 		return $this->inputs[$this->queriedContext][$input]['value'];
 	}
 
+	/** {@inheritdoc} */
 	public function getDescription(){
 		return static::DESCRIPTION;
 	}
 
+	/** {@inheritdoc} */
 	public function getMaintainer(){
 		return static::MAINTAINER;
 	}
 
+	/** {@inheritdoc} */
 	public function getName(){
 		return static::NAME;
 	}
 
+	/** {@inheritdoc} */
 	public function getIcon(){
 		return '';
 	}
 
+	/** {@inheritdoc} */
 	public function getParameters(){
 		return static::PARAMETERS;
 	}
 
+	/** {@inheritdoc} */
 	public function getURI(){
 		return static::URI;
 	}
 
+	/** {@inheritdoc} */
 	public function getCacheTimeout(){
 		return static::CACHE_TIMEOUT;
 	}
diff --git a/lib/BridgeCard.php b/lib/BridgeCard.php
index 28e74fe6..cb7e607b 100644
--- a/lib/BridgeCard.php
+++ b/lib/BridgeCard.php
@@ -1,6 +1,33 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * A generator class for a single bridge card on the home page of RSS-Bridge.
+ *
+ * This class generates the HTML content for a single bridge card for the home
+ * page of RSS-Bridge.
+ *
+ * @todo Return error if a caller creates an object of this class.
+ * @todo Use self:: instead of BridgeCard:: in this class
+ */
 final class BridgeCard {
 
+	/**
+	 * Build a HTML document string of buttons for each of the provided formats
+	 *
+	 * @param array $formats A list of format names
+	 * @return string The document string
+	 */
 	private static function buildFormatButtons($formats) {
 		$buttons = '';
 
@@ -16,6 +43,13 @@ final class BridgeCard {
 		return $buttons;
 	}
 
+	/**
+	 * Get the form header for a bridge card
+	 *
+	 * @param string $bridgeName The bridge name
+	 * @param bool $isHttps If disabled, adds a warning to the form
+	 * @return string The form header
+	 */
 	private static function getFormHeader($bridgeName, $isHttps = false) {
 		$form = <<<EOD
 			<form method="GET" action="?">
@@ -31,6 +65,17 @@ This bridge is not fetching its content through a secure connection</div>';
 		return $form;
 	}
 
+	/**
+	 * Get the form body for a bridge
+	 *
+	 * @param string $bridgeName The bridge name
+	 * @param array $formats A list of supported formats
+	 * @param bool $isActive Indicates if a bridge is enabled or not
+	 * @param bool $isHttps Indicates if a bridge uses HTTPS or not
+	 * @param string $parameterName Sets the bridge context for the current form
+	 * @param array $parameters The bridge parameters
+	 * @return string The form body
+	 */
 	private static function getForm($bridgeName,
 	$formats,
 	$isActive = false,
@@ -88,6 +133,12 @@ This bridge is not fetching its content through a secure connection</div>';
 		return $form . '</form>' . PHP_EOL;
 	}
 
+	/**
+	 * Get input field attributes
+	 *
+	 * @param array $entry The current entry
+	 * @return string The input field attributes
+	 */
 	private static function getInputAttributes($entry) {
 		$retVal = '';
 
@@ -103,6 +154,14 @@ This bridge is not fetching its content through a secure connection</div>';
 		return $retVal;
 	}
 
+	/**
+	 * Get text input
+	 *
+	 * @param array $entry The current entry
+	 * @param string $id The field ID
+	 * @param string $name The field name
+	 * @return string The text input field
+	 */
 	private static function getTextInput($entry, $id, $name) {
 		return '<input '
 		. BridgeCard::getInputAttributes($entry)
@@ -118,6 +177,14 @@ This bridge is not fetching its content through a secure connection</div>';
 		. PHP_EOL;
 	}
 
+	/**
+	 * Get number input
+	 *
+	 * @param array $entry The current entry
+	 * @param string $id The field ID
+	 * @param string $name The field name
+	 * @return string The number input field
+	 */
 	private static function getNumberInput($entry, $id, $name) {
 		return '<input '
 		. BridgeCard::getInputAttributes($entry)
@@ -133,6 +200,14 @@ This bridge is not fetching its content through a secure connection</div>';
 		. PHP_EOL;
 	}
 
+	/**
+	 * Get list input
+	 *
+	 * @param array $entry The current entry
+	 * @param string $id The field ID
+	 * @param string $name The field name
+	 * @return string The list input field
+	 */
 	private static function getListInput($entry, $id, $name) {
 		$list = '<select '
 		. BridgeCard::getInputAttributes($entry)
@@ -185,6 +260,14 @@ This bridge is not fetching its content through a secure connection</div>';
 		return $list;
 	}
 
+	/**
+	 * Get checkbox input
+	 *
+	 * @param array $entry The current entry
+	 * @param string $id The field ID
+	 * @param string $name The field name
+	 * @return string The checkbox input field
+	 */
 	private static function getCheckboxInput($entry, $id, $name) {
 		return '<input '
 		. BridgeCard::getInputAttributes($entry)
@@ -198,6 +281,14 @@ This bridge is not fetching its content through a secure connection</div>';
 		. PHP_EOL;
 	}
 
+	/**
+	 * Gets a single bridge card
+	 *
+	 * @param string $bridgeName The bridge name
+	 * @param array $formats A list of formats
+	 * @param bool $isActive Indicates if the bridge is active or not
+	 * @return string The bridge card
+	 */
 	static function displayBridgeCard($bridgeName, $formats, $isActive = true){
 
 		$bridge = Bridge::create($bridgeName);
diff --git a/lib/BridgeInterface.php b/lib/BridgeInterface.php
index f2ff11d5..bc48fe04 100644
--- a/lib/BridgeInterface.php
+++ b/lib/BridgeInterface.php
@@ -1,4 +1,57 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * The bridge interface
+ *
+ * A bridge is a class that is responsible for collecting and transforming data
+ * from one hosting provider into an internal representation of feed data, that
+ * can later be transformed into different feed formats (see {@see FormatInterface}).
+ *
+ * For this purpose, all bridges need to perform three common operations:
+ *
+ * 1. Collect data from a remote site.
+ * 2. Extract the required contents.
+ * 3. Add the contents to the internal data structure.
+ *
+ * Bridges can optionally specify parameters to customize bridge behavior based
+ * on user input. For example, a user could specify how many items to return in
+ * the feed and where to get them.
+ *
+ * In order to present a bridge on the home page, and for the purpose of bridge
+ * specific behaviour, additional information must be provided by the bridge:
+ *
+ * * **Name**
+ * The name of the bridge that can be displayed to users.
+ *
+ * * **Description**
+ * A brief description for the bridge that can be displayed to users.
+ *
+ * * **URI**
+ * A link to the hosting provider.
+ *
+ * * **Maintainer**
+ * The GitHub username of the bridge maintainer
+ *
+ * * **Parameters**
+ * A list of parameters for customization
+ *
+ * * **Icon**
+ * A link to the favicon of the hosting provider
+ *
+ * * **Cache timeout**
+ * The default cache timeout for the bridge.
+ */
 interface BridgeInterface {
 
 	/**
diff --git a/lib/BridgeList.php b/lib/BridgeList.php
index 1ac7192e..5ff13cf4 100644
--- a/lib/BridgeList.php
+++ b/lib/BridgeList.php
@@ -1,6 +1,31 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * A generator class for the home page of RSS-Bridge.
+ *
+ * This class generates the HTML content for displaying all bridges on the home
+ * page of RSS-Bridge.
+ *
+ * @todo Return error if a caller creates an object of this class.
+ */
 final class BridgeList {
 
+	/**
+	 * Get the document head
+	 *
+	 * @return string The document head
+	 */
 	private static function getHead() {
 		return <<<EOD
 <head>
@@ -22,6 +47,15 @@ final class BridgeList {
 EOD;
 	}
 
+	/**
+	 * Get the document body for all bridge cards
+	 *
+	 * @param bool $showInactive Inactive bridges are visible on the home page if
+	 * enabled.
+	 * @param int $totalBridges (ref) Returns the total number of bridges.
+	 * @param int $totalActiveBridges (ref) Returns the number of active bridges.
+	 * @return string The document body for all bridge cards.
+	 */
 	private static function getBridges($showInactive, &$totalBridges, &$totalActiveBridges) {
 
 		$body = '';
@@ -54,6 +88,11 @@ EOD;
 		return $body;
 	}
 
+	/**
+	 * Get the document header
+	 *
+	 * @return string The document header
+	 */
 	private static function getHeader() {
 		$warning = '';
 
@@ -80,6 +119,11 @@ EOD;
 EOD;
 	}
 
+	/**
+	 * Get the searchbar
+	 *
+	 * @return string The searchbar
+	 */
 	private static function getSearchbar() {
 		$query = filter_input(INPUT_GET, 'q');
 
@@ -93,6 +137,16 @@ EOD;
 EOD;
 	}
 
+	/**
+	 * Get the document footer
+	 *
+	 * @param int $totalBridges The total number of bridges, shown in the footer
+	 * @param int $totalActiveBridges The total number of active bridges, shown
+	 * in the footer.
+	 * @param bool $showInactive Sets the 'Show active'/'Show inactive' text in
+	 * the footer.
+	 * @return string The document footer
+	 */
 	private static function getFooter($totalBridges, $totalActiveBridges, $showInactive) {
 		$version = Configuration::getVersion();
 
@@ -131,6 +185,13 @@ EOD;
 EOD;
 	}
 
+	/**
+	 * Create the entire home page
+	 *
+	 * @param bool $showInactive Inactive bridges are displayed on the home page,
+	 * if enabled.
+	 * @return string The home page
+	 */
 	static function create($showInactive = true) {
 
 		$totalBridges = 0;
diff --git a/lib/CacheInterface.php b/lib/CacheInterface.php
index 5753c0eb..bd2d5613 100644
--- a/lib/CacheInterface.php
+++ b/lib/CacheInterface.php
@@ -1,7 +1,51 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * The cache interface
+ *
+ * @todo Add missing function to the interface
+ * @todo Explain parameters and return values in more detail
+ * @todo Return self more often (to allow call chaining)
+ */
 interface CacheInterface {
+
+	/**
+	 * Loads data from cache
+	 *
+	 * @return mixed The cache data
+	 */
 	public function loadData();
+
+	/**
+	 * Stores data to the cache
+	 *
+	 * @param mixed $datas The data to store
+	 * @return self The cache object
+	 */
 	public function saveData($datas);
+
+	/**
+	 * Returns the timestamp for the curent cache file
+	 *
+	 * @return int Timestamp
+	 */
 	public function getTime();
+
+	/**
+	 * Removes any data that is older than the specified duration from cache
+	 *
+	 * @param int $duration The cache duration in seconds
+	 */
 	public function purgeCache($duration);
 }
diff --git a/lib/Configuration.php b/lib/Configuration.php
index e141ce93..2f17922e 100644
--- a/lib/Configuration.php
+++ b/lib/Configuration.php
@@ -1,10 +1,77 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Configuration module for RSS-Bridge.
+ *
+ * This class implements a configuration module for RSS-Bridge.
+ *
+ * @todo Throw an exception if the caller tries to create objects of this class.
+ * @todo Make this class final.
+ */
 class Configuration {
 
+	/**
+	 * Holds the current release version of RSS-Bridge.
+	 *
+	 * Do not access this property directly!
+	 * Use {@see Configuration::getVersion()} instead.
+	 *
+	 * @var string
+	 *
+	 * @todo Replace this property by a constant.
+	 */
 	public static $VERSION = 'dev.2018-11-10';
 
+	/**
+	 * Holds the configuration data.
+	 *
+	 * Do not access this property directly!
+	 * Use {@see Configuration::getConfig()} instead.
+	 *
+	 * @var array|null
+	 *
+	 * @todo Change the scope of this property to protected or private
+	 */
 	public static $config = null;
 
+	/**
+	 * Verifies the current installation of RSS-Bridge and PHP.
+	 *
+	 * Returns an error message and aborts execution if the installation does
+	 * not satisfy the requirements of RSS-Bridge.
+	 *
+	 * **Requirements**
+	 * - PHP 5.6.0 or higher
+	 * - `openssl` extension
+	 * - `libxml` extension
+	 * - `mbstring` extension
+	 * - `simplexml` extension
+	 * - `curl` extension
+	 * - `json` extension
+	 * - The cache folder specified by {@see PATH_CACHE} requires write permission
+	 * - The whitelist file specified by {@see WHITELIST} requires write permission
+	 *
+	 * @link http://php.net/supported-versions.php PHP Supported Versions
+	 * @link http://php.net/manual/en/book.openssl.php OpenSSL
+	 * @link http://php.net/manual/en/book.libxml.php libxml
+	 * @link http://php.net/manual/en/book.mbstring.php Multibyte String (mbstring)
+	 * @link http://php.net/manual/en/book.simplexml.php SimpleXML
+	 * @link http://php.net/manual/en/book.curl.php Client URL Library (curl)
+	 * @link http://php.net/manual/en/book.json.php JavaScript Object Notation (json)
+	 *
+	 * @return void
+	 */
 	public static function verifyInstallation() {
 
 		// Check PHP version
@@ -40,6 +107,33 @@ class Configuration {
 
 	}
 
+	/**
+	 * Loads the configuration from disk and checks if the parameters are valid.
+	 *
+	 * Returns an error message and aborts execution if the configuration is invalid.
+	 *
+	 * The RSS-Bridge configuration is split into two files:
+	 * - `config.default.ini.php`: The default configuration file that ships with
+	 * every release of RSS-Bridge (do not modify this file!).
+	 * - `config.ini.php`: The local configuration file that can be modified by
+	 * server administrators.
+	 *
+	 * RSS-Bridge will first load `config.default.ini.php` into memory and then
+	 * replace parameters with the contents of `config.ini.php`. That way new
+	 * parameters are automatically initialized with default values and custom
+	 * configurations can be reduced to the minimum set of parametes necessary
+	 * (only the ones that changed).
+	 *
+	 * The configuration files must be placed in the root folder of RSS-Bridge
+	 * (next to `index.php`).
+	 *
+	 * _Notice_: The configuration is stored in {@see Configuration::$config}.
+	 *
+	 * @return void
+	 *
+	 * @todo Use {@see PATH_ROOT} to locate configuration files.
+	 * @todo Add documentation for constants defined by this function.
+	 */
 	public static function loadConfiguration() {
 
 		if(!file_exists('config.default.ini.php'))
@@ -97,6 +191,15 @@ class Configuration {
 
 	}
 
+	/**
+	 * Returns the value of a parameter identified by category and key.
+	 *
+	 * @param string $category The section name (category).
+	 * @param string $key The property name (key).
+	 * @return mixed|null The parameter value.
+	 *
+	 * @todo Rename $category to $section for clarity.
+	 */
 	public static function getConfig($category, $key) {
 
 		if(array_key_exists($category, self::$config) && array_key_exists($key, self::$config[$category])) {
@@ -107,6 +210,15 @@ class Configuration {
 
 	}
 
+	/**
+	 * Returns the current version string of RSS-Bridge.
+	 *
+	 * This function returns the contents of {@see Configuration::$VERSION} for
+	 * regular installations and the git branch name and commit id for instances
+	 * running in a git environment.
+	 *
+	 * @return string The version string.
+	 */
 	public static function getVersion() {
 
 		$headFile = '.git/HEAD';
diff --git a/lib/Exceptions.php b/lib/Exceptions.php
index 32b33f2b..e9b4d7b8 100644
--- a/lib/Exceptions.php
+++ b/lib/Exceptions.php
@@ -1,17 +1,35 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Implements a RSS-Bridge specific exception class
+ *
+ * @todo This class serves no purpose, remove it!
+ */
 class HttpException extends \Exception{}
 
 /**
  * Returns an URL that automatically populates a new issue on GitHub based
  * on the information provided
  *
- * @param $title string Sets the title of the issue
- * @param $body string Sets the body of the issue (GitHub markdown applies)
- * @param $labels mixed (optional) Specifies labels to add to the issue
- * @param $maintainer string (optional) Specifies the maintainer for the issue.
+ * @param string $title string Sets the title of the issue
+ * @param string $body string Sets the body of the issue (GitHub markdown applies)
+ * @param string $labels mixed (optional) Specifies labels to add to the issue
+ * @param string $maintainer string (optional) Specifies the maintainer for the issue.
  * The maintainer only applies if part of the development team!
- * @return string Returns a qualified URL to a new issue with populated conent.
- * Returns null if title or body is null or empty
+ * @return string|null A qualified URL to a new issue with populated conent or null.
+ *
+ * @todo This function belongs inside a class
  */
 function buildGitHubIssueQuery($title, $body, $labels = null, $maintainer = null){
 	if(!isset($title) || !isset($body) || empty($title) || empty($body)) {
@@ -49,10 +67,11 @@ function buildGitHubIssueQuery($title, $body, $labels = null, $maintainer = null
 /**
  * Returns the exception message as HTML string
  *
- * @param $e Exception The exception to show
- * @param $bridge object The bridge object
- * @return string Returns the exception as HTML string. Returns null if the
- * provided parameter are invalid
+ * @param object $e Exception The exception to show
+ * @param object $bridge object The bridge object
+ * @return string|null Returns the exception as HTML string or null.
+ *
+ * @todo This function belongs inside a class
  */
 function buildBridgeException($e, $bridge){
 	if(( !($e instanceof \Exception) && !($e instanceof \Error)) || !($bridge instanceof \BridgeInterface)) {
@@ -87,10 +106,11 @@ EOD;
 /**
  * Returns the exception message as HTML string
  *
- * @param $e Exception The exception to show
- * @param $bridge object The bridge object
- * @return string Returns the exception as HTML string. Returns null if the
- * provided parameter are invalid
+ * @param object $e Exception The exception to show
+ * @param object $bridge object The bridge object
+ * @return string|null Returns the exception as HTML string or null.
+ *
+ * @todo This function belongs inside a class
  */
 function buildTransformException($e, $bridge){
 	if(( !($e instanceof \Exception) && !($e instanceof \Error)) || !($bridge instanceof \BridgeInterface)) {
@@ -114,6 +134,15 @@ function buildTransformException($e, $bridge){
 	return buildPage($title, $header, $section);
 }
 
+/**
+ * Builds a new HTML header with data from a exception an a bridge
+ *
+ * @param object $e The exception object
+ * @param object $bridge The bridge object
+ * @return string The HTML header
+ *
+ * @todo This function belongs inside a class
+ */
 function buildHeader($e, $bridge){
 	return <<<EOD
 <header>
@@ -124,6 +153,17 @@ function buildHeader($e, $bridge){
 EOD;
 }
 
+/**
+ * Builds a new HTML section
+ *
+ * @param object $e The exception object
+ * @param object $bridge The bridge object
+ * @param string $message The message to display
+ * @param string $link The link to include in the anchor
+ * @return string The HTML section
+ *
+ * @todo This function belongs inside a class
+ */
 function buildSection($e, $bridge, $message, $link){
 	return <<<EOD
 <section>
@@ -142,6 +182,16 @@ function buildSection($e, $bridge, $message, $link){
 EOD;
 }
 
+/**
+ * Builds a new HTML page
+ *
+ * @param string $title The HTML title
+ * @param string $header The HTML header
+ * @param string $section The HTML section
+ * @return string The HTML page
+ *
+ * @todo This function belongs inside a class
+ */
 function buildPage($title, $header, $section){
 	return <<<EOD
 <!DOCTYPE html>
diff --git a/lib/FeedExpander.php b/lib/FeedExpander.php
index 893c3ba1..04f835aa 100644
--- a/lib/FeedExpander.php
+++ b/lib/FeedExpander.php
@@ -1,11 +1,74 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
 
+/**
+ * An abstract class for bridges that need to transform existing RSS or Atom
+ * feeds.
+ *
+ * This class extends {@see BridgeAbstract} with functions to extract contents
+ * from existing RSS or Atom feeds. Bridges that need to transform existing feeds
+ * should inherit from this class instead of {@see BridgeAbstract}.
+ *
+ * Bridges that extend this class don't need to concern themselves with getting
+ * contents from existing feeds, but can focus on adding additional contents
+ * (i.e. by downloading additional data), filtering or just transforming a feed
+ * into another format.
+ *
+ * @link http://www.rssboard.org/rss-0-9-1 RSS 0.91 Specification
+ * @link http://web.resource.org/rss/1.0/spec RDF Site Summary (RSS) 1.0
+ * @link http://www.rssboard.org/rss-specification RSS 2.0 Specification
+ * @link https://tools.ietf.org/html/rfc4287 The Atom Syndication Format
+ *
+ * @todo Return `self` on more functions to allow chaining
+ * @todo The parsing functions should all be private. This class is complicated
+ * enough without having to consider children overriding functions.
+ */
 abstract class FeedExpander extends BridgeAbstract {
 
+	/**
+	 * Holds the title of the current feed
+	 *
+	 * @var string
+	 * @todo Rename this parameter to $title for clarity
+	 */
 	private $name;
+
+	/**
+	 * Holds the URI of the feed
+	 *
+	 * @var string
+	 */
 	private $uri;
+
+	/**
+	 * Holds the feed type during internal operations.
+	 *
+	 * @var string
+	 * @todo Define possible values as constant instead of static strings
+	 */
 	private $feedType;
 
+	/**
+	 * Collects data from an existing feed.
+	 *
+	 * Children should call this function in {@see BridgeInterface::collectData()}
+	 * to extract a feed.
+	 *
+	 * @param string $url URL to the feed.
+	 * @param int $maxItems Maximum number of items to collect from the feed
+	 * (`-1`: no limit).
+	 * @return void
+	 */
 	public function collectExpandableDatas($url, $maxItems = -1){
 		if(empty($url)) {
 			returnServerError('There is no $url for this RSS expander');
@@ -44,6 +107,19 @@ abstract class FeedExpander extends BridgeAbstract {
 		$this->{'collect_' . $this->feedType . '_data'}($rssContent, $maxItems);
 	}
 
+	/**
+	 * Collect data from a RSS 1.0 compatible feed
+	 *
+	 * @link http://web.resource.org/rss/1.0/spec RDF Site Summary (RSS) 1.0
+	 *
+	 * @param string $rssContent The RSS content
+	 * @param int $maxItems Maximum number of items to collect from the feed
+	 * (`-1`: no limit).
+	 * @return void
+	 *
+	 * @todo Instead of passing $maxItems to all functions, just add all items
+	 * and remove excessive items later.
+	 */
 	protected function collect_RSS_1_0_data($rssContent, $maxItems){
 		$this->load_RSS_2_0_feed_data($rssContent->channel[0]);
 		foreach($rssContent->item as $item) {
@@ -56,6 +132,19 @@ abstract class FeedExpander extends BridgeAbstract {
 		}
 	}
 
+	/**
+	 * Collect data from a RSS 2.0 compatible feed
+	 *
+	 * @link http://www.rssboard.org/rss-specification RSS 2.0 Specification
+	 *
+	 * @param object $rssContent The RSS content
+	 * @param int $maxItems Maximum number of items to collect from the feed
+	 * (`-1`: no limit).
+	 * @return void
+	 *
+	 * @todo Instead of passing $maxItems to all functions, just add all items
+	 * and remove excessive items later.
+	 */
 	protected function collect_RSS_2_0_data($rssContent, $maxItems){
 		$rssContent = $rssContent->channel[0];
 		Debug::log('RSS content is ===========\n'
@@ -73,6 +162,19 @@ abstract class FeedExpander extends BridgeAbstract {
 		}
 	}
 
+	/**
+	 * Collect data from a Atom 1.0 compatible feed
+	 *
+	 * @link https://tools.ietf.org/html/rfc4287  The Atom Syndication Format
+	 *
+	 * @param object $content The Atom content
+	 * @param int $maxItems Maximum number of items to collect from the feed
+	 * (`-1`: no limit).
+	 * @return void
+	 *
+	 * @todo Instead of passing $maxItems to all functions, just add all items
+	 * and remove excessive items later.
+	 */
 	protected function collect_ATOM_1_0_data($content, $maxItems){
 		$this->load_ATOM_feed_data($content);
 		foreach($content->entry as $item) {
@@ -85,16 +187,35 @@ abstract class FeedExpander extends BridgeAbstract {
 		}
 	}
 
+	/**
+	 * Convert RSS 2.0 time to timestamp
+	 *
+	 * @param object $item A feed item
+	 * @return int The timestamp
+	 */
 	protected function RSS_2_0_time_to_timestamp($item){
 		return DateTime::createFromFormat('D, d M Y H:i:s e', $item->pubDate)->getTimestamp();
 	}
 
-	// TODO set title, link, description, language, and so on
+	/**
+	 * Load RSS 2.0 feed data into RSS-Bridge
+	 *
+	 * @param object $rssContent The RSS content
+	 * @return void
+	 *
+	 * @todo set title, link, description, language, and so on
+	 */
 	protected function load_RSS_2_0_feed_data($rssContent){
 		$this->name = trim((string)$rssContent->title);
 		$this->uri = trim((string)$rssContent->link);
 	}
 
+	/**
+	 * Load Atom feed data into RSS-Bridge
+	 *
+	 * @param object $content The Atom content
+	 * @return void
+	 */
 	protected function load_ATOM_feed_data($content){
 		$this->name = (string)$content->title;
 
@@ -114,6 +235,16 @@ abstract class FeedExpander extends BridgeAbstract {
 		}
 	}
 
+	/**
+	 * Parse the contents of a single Atom feed item into a RSS-Bridge item for
+	 * further transformation.
+	 *
+	 * @param object $feedItem A single feed item
+	 * @return object The RSS-Bridge item
+	 *
+	 * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
+	 * of its own?
+	 */
 	protected function parseATOMItem($feedItem){
 		// Some ATOM entries also contain RSS 2.0 fields
 		$item = $this->parseRSS_2_0_Item($feedItem);
@@ -139,6 +270,16 @@ abstract class FeedExpander extends BridgeAbstract {
 		return $item;
 	}
 
+	/**
+	 * Parse the contents of a single RSS 0.91 feed item into a RSS-Bridge item
+	 * for further transformation.
+	 *
+	 * @param object $feedItem A single feed item
+	 * @return object The RSS-Bridge item
+	 *
+	 * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
+	 * of its own?
+	 */
 	protected function parseRSS_0_9_1_Item($feedItem){
 		$item = array();
 		if(isset($feedItem->link)) $item['uri'] = (string)$feedItem->link;
@@ -150,6 +291,16 @@ abstract class FeedExpander extends BridgeAbstract {
 		return $item;
 	}
 
+	/**
+	 * Parse the contents of a single RSS 1.0 feed item into a RSS-Bridge item
+	 * for further transformation.
+	 *
+	 * @param object $feedItem A single feed item
+	 * @return object The RSS-Bridge item
+	 *
+	 * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
+	 * of its own?
+	 */
 	protected function parseRSS_1_0_Item($feedItem){
 		// 1.0 adds optional elements around the 0.91 standard
 		$item = $this->parseRSS_0_9_1_Item($feedItem);
@@ -164,6 +315,16 @@ abstract class FeedExpander extends BridgeAbstract {
 		return $item;
 	}
 
+	/**
+	 * Parse the contents of a single RSS 2.0 feed item into a RSS-Bridge item
+	 * for further transformation.
+	 *
+	 * @param object $feedItem A single feed item
+	 * @return object The RSS-Bridge item
+	 *
+	 * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
+	 * of its own?
+	 */
 	protected function parseRSS_2_0_Item($feedItem){
 		// Primary data is compatible to 0.91 with some additional data
 		$item = $this->parseRSS_0_9_1_Item($feedItem);
@@ -211,9 +372,11 @@ abstract class FeedExpander extends BridgeAbstract {
 	}
 
 	/**
-	 * Method should return, from a source RSS item given by lastRSS, one of our Items objects
-	 * @param $item the input rss item
-	 * @return a RSS-Bridge Item, with (hopefully) the whole content)
+	 * Parse the contents of a single feed item, depending on the current feed
+	 * type, into a RSS-Bridge item.
+	 *
+	 * @param object $item The current feed item
+	 * @return object A RSS-Bridge item, with (hopefully) the whole content
 	 */
 	protected function parseItem($item){
 		switch($this->feedType) {
@@ -230,14 +393,17 @@ abstract class FeedExpander extends BridgeAbstract {
 		}
 	}
 
+	/** {@inheritdoc} */
 	public function getURI(){
 		return !empty($this->uri) ? $this->uri : parent::getURI();
 	}
 
+	/** {@inheritdoc} */
 	public function getName(){
 		return !empty($this->name) ? $this->name : parent::getName();
 	}
 
+	/** {@inheritdoc} */
 	public function getIcon(){
 		return !empty($this->icon) ? $this->icon : parent::getIcon();
 	}
diff --git a/lib/FormatAbstract.php b/lib/FormatAbstract.php
index 8fb642c0..3315666d 100644
--- a/lib/FormatAbstract.php
+++ b/lib/FormatAbstract.php
@@ -1,41 +1,95 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	https://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
 
+/**
+ * An abstract class for format implementations
+ *
+ * This class implements {@see FormatInterface}
+ */
 abstract class FormatAbstract implements FormatInterface {
+
+	/** The default charset (UTF-8) */
 	const DEFAULT_CHARSET = 'UTF-8';
 
-	protected
-		$contentType,
-		$charset,
-		$items,
-		$lastModified,
-		$extraInfos;
+	/** @var string $contentType The content type */
+	protected $contentType;
 
+	/** @var string $charset The charset */
+	protected $charset;
+
+	/** @var array $items The items */
+	protected $items;
+
+	/**
+	 * @var int $lastModified A timestamp to indicate the last modified time of
+	 * the output data.
+	 */
+	protected $lastModified;
+
+	/** @var array $extraInfos The extra infos */
+	protected $extraInfos;
+
+	/**
+	 * {@inheritdoc}
+	 *
+	 * @param string $charset {@inheritdoc}
+	 */
 	public function setCharset($charset){
 		$this->charset = $charset;
 
 		return $this;
 	}
 
+	/** {@inheritdoc} */
 	public function getCharset(){
 		$charset = $this->charset;
 
 		return is_null($charset) ? static::DEFAULT_CHARSET : $charset;
 	}
 
+	/**
+	 * Set the content type
+	 *
+	 * @param string $contentType The content type
+	 * @return self The format object
+	 */
 	protected function setContentType($contentType){
 		$this->contentType = $contentType;
 
 		return $this;
 	}
 
+	/**
+	 * Set the last modified time
+	 *
+	 * @param int $lastModified The last modified time
+	 * @return void
+	 */
 	public function setLastModified($lastModified){
 		$this->lastModified = $lastModified;
 	}
 
+	/**
+	 * Send header with the currently specified content type
+	 *
+	 * @return void
+	 * @todo This should throw an error if no content type is set
+	 */
 	protected function callContentType(){
 		header('Content-Type: ' . $this->contentType);
 	}
 
+	/** {@inheritdoc} */
 	public function display(){
 		if ($this->lastModified) {
 			header('Last-Modified: ' . gmdate('D, d M Y H:i:s ', $this->lastModified) . 'GMT');
@@ -45,12 +99,18 @@ abstract class FormatAbstract implements FormatInterface {
 		return $this;
 	}
 
+	/**
+	 * {@inheritdoc}
+	 *
+	 * @param array $items {@inheritdoc}
+	 */
 	public function setItems(array $items){
 		$this->items = array_map(array($this, 'array_trim'), $items);
 
 		return $this;
 	}
 
+	/** {@inheritdoc} */
 	public function getItems(){
 		if(!is_array($this->items))
 			throw new \LogicException('Feed the ' . get_class($this) . ' with "setItems" method before !');
@@ -59,10 +119,10 @@ abstract class FormatAbstract implements FormatInterface {
 	}
 
 	/**
-	* Define common informations can be required by formats and set default value for unknown values
-	* @param array $extraInfos array with know informations (there isn't merge !!!)
-	* @return this
-	*/
+	 * {@inheritdoc}
+	 *
+	 * @param array $extraInfos {@inheritdoc}
+	 */
 	public function setExtraInfos(array $extraInfos = array()){
 		foreach(array('name', 'uri', 'icon') as $infoName) {
 			if(!isset($extraInfos[$infoName])) {
@@ -75,10 +135,7 @@ abstract class FormatAbstract implements FormatInterface {
 		return $this;
 	}
 
-	/**
-	* Return extra infos
-	* @return array See "setExtraInfos" detail method to know what extra are disponibles
-	*/
+	/** {@inheritdoc} */
 	public function getExtraInfos(){
 		if(is_null($this->extraInfos)) { // No extra info ?
 			$this->setExtraInfos(); // Define with default value
@@ -88,12 +145,17 @@ abstract class FormatAbstract implements FormatInterface {
 	}
 
 	/**
-	 * Sanitized html while leaving it functionnal.
-	 * The aim is to keep html as-is (with clickable hyperlinks)
-	 * while reducing annoying and potentially dangerous things.
-	 * Yes, I know sanitizing HTML 100% is an impossible task.
-	 * Maybe we'll switch to http://htmlpurifier.org/
-	 * or http://www.bioinformatics.org/phplabware/internal_utilities/htmLawed/index.php
+	 * Sanitize HTML while leaving it functional.
+	 *
+	 * Keeps HTML as-is (with clickable hyperlinks) while reducing annoying and
+	 * potentially dangerous things.
+	 *
+	 * @param string $html The HTML content
+	 * @return string The sanitized HTML content
+	 *
+	 * @todo This belongs into `html.php`
+	 * @todo Maybe switch to http://htmlpurifier.org/
+	 * @todo Maybe switch to http://www.bioinformatics.org/phplabware/internal_utilities/htmLawed/index.php
 	 */
 	protected function sanitizeHtml($html)
 	{
@@ -104,6 +166,17 @@ abstract class FormatAbstract implements FormatInterface {
 		return $html;
 	}
 
+	/**
+	 * Trim each element of an array
+	 *
+	 * This function applies `trim()` to all elements in the array, if the element
+	 * is a valid string.
+	 *
+	 * @param array $elements The array to trim
+	 * @return array The trimmed array
+	 *
+	 * @todo This is a utility function that doesn't belong here, find a new home.
+	 */
 	protected function array_trim($elements){
 		foreach($elements as $key => $value) {
 			if(is_string($value))
diff --git a/lib/FormatInterface.php b/lib/FormatInterface.php
index f99d214f..d59a4ef9 100644
--- a/lib/FormatInterface.php
+++ b/lib/FormatInterface.php
@@ -1,11 +1,84 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * The format interface
+ *
+ * @todo Add missing function to the interface
+ * @todo Explain parameters and return values in more detail
+ * @todo Return self more often (to allow call chaining)
+ */
 interface FormatInterface {
+
+	/**
+	 * Generate a string representation of the current data
+	 *
+	 * @return string The string representation
+	 */
 	public function stringify();
+
+	/**
+	 * Display the current data to the user
+	 *
+	 * @return self The format object
+	 */
 	public function display();
+
+	/**
+	 * Set items
+	 *
+	 * @param array $bridges The items
+	 * @return self The format object
+	 *
+	 * @todo Rename parameter `$bridges` to `$items`
+	 */
 	public function setItems(array $bridges);
+
+	/**
+	 * Return items
+	 *
+	 * @throws \LogicException if the items are not set
+	 * @return array The items
+	 */
 	public function getItems();
+
+	/**
+	 * Set extra information
+	 *
+	 * @param array $infos Extra information
+	 * @return self The format object
+	 */
 	public function setExtraInfos(array $infos);
+
+	/**
+	 * Return extra information
+	 *
+	 * @return array Extra information
+	 */
 	public function getExtraInfos();
+
+	/**
+	 * Set charset
+	 *
+	 * @param string $charset The charset
+	 * @return self The format object
+	 */
 	public function setCharset($charset);
+
+	/**
+	 * Return current charset
+	 *
+	 * @return string The charset
+	 */
 	public function getCharset();
 }
diff --git a/lib/ParameterValidator.php b/lib/ParameterValidator.php
index c278e4d1..91fe7c92 100644
--- a/lib/ParameterValidator.php
+++ b/lib/ParameterValidator.php
@@ -1,10 +1,35 @@
 <?php
 /**
- * Implements a validator for bridge parameters
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Validator for bridge parameters
  */
 class ParameterValidator {
+
+	/**
+	 * Holds the list of invalid parameters
+	 *
+	 * @var array
+	 */
 	private $invalid = array();
 
+	/**
+	 * Add item to list of invalid parameters
+	 *
+	 * @param string $name The name of the parameter
+	 * @param string $reason The reason for that parameter being invalid
+	 * @return void
+	 */
 	private function addInvalidParameter($name, $reason){
 		$this->invalid[] = array(
 			'name' => $name,
@@ -13,13 +38,23 @@ class ParameterValidator {
 	}
 
 	/**
-	 * Returns an array of invalid parameters, where each element is an
-	 * array of 'name' and 'reason'.
+	 * Return list of invalid parameters.
+	 *
+	 * Each element is an array of 'name' and 'reason'.
+	 *
+	 * @return array List of invalid parameters
 	 */
 	public function getInvalidParameters() {
 		return $this->invalid;
 	}
 
+	/**
+	 * Validate value for a text input
+	 *
+	 * @param string $value The value of a text input
+	 * @param string|null $pattern (optional) A regex pattern
+	 * @return string|null The filtered value or null if the value is invalid
+	 */
 	private function validateTextValue($value, $pattern = null){
 		if(!is_null($pattern)) {
 			$filteredValue = filter_var($value,
@@ -38,6 +73,12 @@ class ParameterValidator {
 		return $filteredValue;
 	}
 
+	/**
+	 * Validate value for a number input
+	 *
+	 * @param int $value The value of a number input
+	 * @return int|null The filtered value or null if the value is invalid
+	 */
 	private function validateNumberValue($value){
 		$filteredValue = filter_var($value, FILTER_VALIDATE_INT);
 
@@ -47,10 +88,23 @@ class ParameterValidator {
 		return $filteredValue;
 	}
 
+	/**
+	 * Validate value for a checkbox
+	 *
+	 * @param bool $value The value of a checkbox
+	 * @return bool The filtered value
+	 */
 	private function validateCheckboxValue($value){
 		return filter_var($value, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);
 	}
 
+	/**
+	 * Validate value for a list
+	 *
+	 * @param string $value The value of a list
+	 * @param array $expectedValues A list of expected values
+	 * @return string|null The filtered value or null if the value is invalid
+	 */
 	private function validateListValue($value, $expectedValues){
 		$filteredValue = filter_var($value);
 
@@ -69,9 +123,11 @@ class ParameterValidator {
 	}
 
 	/**
-	 * Checks if all required parameters are supplied by the user
-	 * @param $data An array of parameters provided by the user
-	 * @param $parameters An array of bridge parameters
+	 * Check if all required parameters are satisfied
+	 *
+	 * @param array $data (ref) A list of input values
+	 * @param array $parameters The bridge parameters
+	 * @return bool True if all parameters are satisfied
 	 */
 	public function validateData(&$data, $parameters){
 
@@ -122,11 +178,11 @@ class ParameterValidator {
 	}
 
 	/**
-	 * Returns the name of the context matching the provided inputs
+	 * Get the name of the context matching the provided inputs
 	 *
 	 * @param array $data Associative array of user data
 	 * @param array $parameters Array of bridge parameters
-	 * @return mixed Returns the context name or null if no match was found
+	 * @return string|null Returns the context name or null if no match was found
 	 */
 	public function getQueriedContext($data, $parameters){
 		$queriedContexts = array();
diff --git a/lib/contents.php b/lib/contents.php
index fbd93f1b..127638bc 100644
--- a/lib/contents.php
+++ b/lib/contents.php
@@ -1,4 +1,31 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Gets contents from the Internet.
+ *
+ * @param string $url The URL.
+ * @param array $header (optional) A list of cURL header.
+ * For more information follow the links below.
+ * * https://php.net/manual/en/function.curl-setopt.php
+ * * https://curl.haxx.se/libcurl/c/CURLOPT_HTTPHEADER.html
+ * @param array $opts (optional) A list of cURL options as associative array in
+ * the format `$opts[$option] = $value;`, where `$option` is any `CURLOPT_XXX`
+ * option and `$value` the corresponding value.
+ *
+ * For more information see http://php.net/manual/en/function.curl-setopt.php
+ * @return string The contents.
+ */
 function getContents($url, $header = array(), $opts = array()){
 	Debug::log('Reading contents from "' . $url . '"');
 
@@ -74,6 +101,32 @@ EOD
 	return substr($data, $headerSize);
 }
 
+/**
+ * Gets contents from the Internet as simplhtmldom object.
+ *
+ * @param string $url The URL.
+ * @param array $header (optional) A list of cURL header.
+ * For more information follow the links below.
+ * * https://php.net/manual/en/function.curl-setopt.php
+ * * https://curl.haxx.se/libcurl/c/CURLOPT_HTTPHEADER.html
+ * @param array $opts (optional) A list of cURL options as associative array in
+ * the format `$opts[$option] = $value;`, where `$option` is any `CURLOPT_XXX`
+ * option and `$value` the corresponding value.
+ *
+ * For more information see http://php.net/manual/en/function.curl-setopt.php
+ * @param bool $lowercase Force all selectors to lowercase.
+ * @param bool $forceTagsClosed Forcefully close tags in malformed HTML.
+ *
+ * _Remarks_: Forcefully closing tags is great for malformed HTML, but it can
+ * lead to parsing errors.
+ * @param string $target_charset Defines the target charset.
+ * @param bool $stripRN Replace all occurrences of `"\r"` and `"\n"` by `" "`.
+ * @param string $defaultBRText Specifies the replacement text for `<br>` tags
+ * when returning plaintext.
+ * @param string $defaultSpanText Specifies the replacement text for `<span />`
+ * tags when returning plaintext.
+ * @return string Contents as simplehtmldom object.
+ */
 function getSimpleHTMLDOM($url,
 $header = array(),
 $opts = array(),
@@ -94,10 +147,34 @@ $defaultSpanText = DEFAULT_SPAN_TEXT){
 }
 
 /**
- * Maintain locally cached versions of pages to avoid multiple downloads.
- * @param url url to cache
- * @param duration duration of the cache file in seconds (default: 24h/86400s)
- * @return content of the file as string
+ * Gets contents from the Internet as simplhtmldom object. Contents are cached
+ * and re-used for subsequent calls until the cache duration elapsed.
+ *
+ * _Notice_: Cached contents are forcefully removed after 24 hours (86400 seconds).
+ *
+ * @param string $url The URL.
+ * @param int $duration Cache duration in seconds.
+ * @param array $header (optional) A list of cURL header.
+ * For more information follow the links below.
+ * * https://php.net/manual/en/function.curl-setopt.php
+ * * https://curl.haxx.se/libcurl/c/CURLOPT_HTTPHEADER.html
+ * @param array $opts (optional) A list of cURL options as associative array in
+ * the format `$opts[$option] = $value;`, where `$option` is any `CURLOPT_XXX`
+ * option and `$value` the corresponding value.
+ *
+ * For more information see http://php.net/manual/en/function.curl-setopt.php
+ * @param bool $lowercase Force all selectors to lowercase.
+ * @param bool $forceTagsClosed Forcefully close tags in malformed HTML.
+ *
+ * _Remarks_: Forcefully closing tags is great for malformed HTML, but it can
+ * lead to parsing errors.
+ * @param string $target_charset Defines the target charset.
+ * @param bool $stripRN Replace all occurrences of `"\r"` and `"\n"` by `" "`.
+ * @param string $defaultBRText Specifies the replacement text for `<br>` tags
+ * when returning plaintext.
+ * @param string $defaultSpanText Specifies the replacement text for `<span />`
+ * tags when returning plaintext.
+ * @return string Contents as simplehtmldom object.
  */
 function getSimpleHTMLDOMCached($url,
 $duration = 86400,
@@ -142,9 +219,12 @@ $defaultSpanText = DEFAULT_SPAN_TEXT){
 }
 
 /**
- * Parses the provided response header into an associative array
+ * Parses the cURL response header into an associative array
  *
  * Based on https://stackoverflow.com/a/18682872
+ *
+ * @param string $header The cURL response header.
+ * @return array An associative array of response headers.
  */
 function parseResponseHeader($header) {
 
@@ -177,10 +257,18 @@ function parseResponseHeader($header) {
 }
 
 /**
- * Determine MIME type from URL/Path file extension
- * Remark: Built-in functions mime_content_type or fileinfo requires fetching remote content
- * Remark: A bridge can hint for a MIME type by appending #.ext to a URL, e.g. #.image
+ * Determines the MIME type from a URL/Path file extension.
+ *
+ * _Remarks_:
+ *
+ * * The built-in functions `mime_content_type` and `fileinfo` require fetching
+ * remote contents.
+ * * A caller can hint for a MIME type by appending `#.ext` to the URL (i.e. `#.image`).
+ *
  * Based on https://stackoverflow.com/a/1147952
+ *
+ * @param string $url The URL or path to the file.
+ * @return string The MIME type of the file.
  */
 function getMimeType($url) {
 	static $mime = null;
diff --git a/lib/error.php b/lib/error.php
index abf3c2db..8546f6cd 100644
--- a/lib/error.php
+++ b/lib/error.php
@@ -1,12 +1,43 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Throws an exception when called.
+ *
+ * @throws \HttpException when called
+ * @param string $message The error message
+ * @param int $code The HTTP error code
+ * @link https://en.wikipedia.org/wiki/List_of_HTTP_status_codes List of HTTP
+ * status codes
+ */
 function returnError($message, $code){
 	throw new \HttpException($message, $code);
 }
 
+/**
+ * Returns HTTP Error 400 (Bad Request) when called.
+ *
+ * @param string $message The error message
+ */
 function returnClientError($message){
 	returnError($message, 400);
 }
 
+/**
+ * Returns HTTP Error 500 (Internal Server Error) when called.
+ *
+ * @param string $message The error message
+ */
 function returnServerError($message){
 	returnError($message, 500);
 }
diff --git a/lib/html.php b/lib/html.php
index f87991f1..a9eccef6 100644
--- a/lib/html.php
+++ b/lib/html.php
@@ -1,4 +1,34 @@
 <?php
+/**
+ * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
+ * Atom feeds for websites that don't have one.
+ *
+ * For the full license information, please view the UNLICENSE file distributed
+ * with this source code.
+ *
+ * @package	Core
+ * @license	http://unlicense.org/ UNLICENSE
+ * @link	https://github.com/rss-bridge/rss-bridge
+ */
+
+/**
+ * Removes unwanted tags from a given HTML text.
+ *
+ * @param string $textToSanitize The HTML text to sanitize.
+ * @param array $removedTags A list of tags to remove from the DOM.
+ * @param array $keptAttributes A list of attributes to keep on tags (other
+ * attributes are removed).
+ * @param array $keptText A list of tags where the innertext replaces the tag
+ * (i.e. `<p>Hello World!</p>` becomes `Hello World!`).
+ * @return object A simplehtmldom object of the remaining contents.
+ *
+ * @todo Check if this implementation is still necessary, because simplehtmldom
+ * already removes some of the tags (search for `remove_noise` in simple_html_dom.php).
+ * @todo Rename parameters to make more sense. `$textToSanitize` must be HTML,
+ * `$removedTags`, `$keptAttributes` and `$keptText` are past tense.
+ * @todo Clarify the meaning of `*[!b38fd2b1fe7f4747d6b1c1254ccd055e]`, which
+ * looks like a SHA1 hash (does simplehtmldom not support `find('*')`?).
+ */
 function sanitize($textToSanitize,
 $removedTags = array('script', 'iframe', 'input', 'form'),
 $keptAttributes = array('title', 'href', 'src'),
@@ -21,6 +51,35 @@ $keptText = array()){
 	return $htmlContent;
 }
 
+/**
+ * Replace background by image
+ *
+ * Replaces tags with styles of `backgroud-image` by `<img />` tags.
+ *
+ * For example:
+ *
+ * ```HTML
+ * <html>
+ *   <body style="background-image: url('bgimage.jpg');">
+ *     <h1>Hello world!</h1>
+ *   </body>
+ * </html>
+ * ```
+ *
+ * results in this output:
+ *
+ * ```HTML
+ * <html>
+ *   <img style="display:block;" src="bgimage.jpg" />
+ * </html>
+ * ```
+ *
+ * @param string $htmlContent The HTML content
+ * @return string The HTML content with all ocurrences replaced
+ *
+ * @todo Clarify the meaning of `*[!b38fd2b1fe7f4747d6b1c1254ccd055e]`, which
+ * looks like a SHA1 hash (does simplehtmldom not support `find('*')`?).
+ */
 function backgroundToImg($htmlContent) {
 
 	$regex = '/background-image[ ]{0,}:[ ]{0,}url\([\'"]{0,}(.*?)[\'"]{0,}\)/';
@@ -42,9 +101,17 @@ function backgroundToImg($htmlContent) {
 
 /**
  * Convert relative links in HTML into absolute links
- * @param $content HTML content to fix. Supports HTML objects or string objects
- * @param $server full URL to the page containing relative links
- * @return content with fixed URLs, as HTML object or string depending on input type
+ *
+ * This function is based on `php-urljoin`.
+ *
+ * @link https://github.com/plaidfluff/php-urljoin php-urljoin
+ *
+ * @param string|object $content The HTML content. Supports HTML objects or string objects
+ * @param string $server Fully qualified URL to the page containing relative links
+ * @return object Content with fixed URLs.
+ *
+ * @todo If the input type was a string, this function should return a string as
+ * well. This is currently done implicitly by how the simplehtmldom object works.
  */
 function defaultLinkTo($content, $server){
 	$string_convert = false;
@@ -70,10 +137,14 @@ function defaultLinkTo($content, $server){
 
 /**
  * Extract the first part of a string matching the specified start and end delimiters
- * @param $string input string, e.g. '<div>Post author: John Doe</div>'
- * @param $start start delimiter, e.g. 'author: '
- * @param $end end delimiter, e.g. '<'
- * @return extracted string, e.g. 'John Doe', or false if the delimiters were not found.
+ *
+ * @param string $string Input string, e.g. `<div>Post author: John Doe</div>`
+ * @param string $start Start delimiter, e.g. `author: `
+ * @param string $end End delimiter, e.g. `<`
+ * @return string|bool Extracted string, e.g. `John Doe`, or false if the
+ * delimiters were not found.
+ *
+ * @todo This function can possibly be simplified to use a single `substr` command.
  */
 function extractFromDelimiters($string, $start, $end) {
 	if (strpos($string, $start) !== false) {
@@ -85,10 +156,13 @@ function extractFromDelimiters($string, $start, $end) {
 
 /**
  * Remove one or more part(s) of a string using a start and end delmiters
- * @param $string input string, e.g. 'foo<script>superscript()</script>bar'
- * @param $start start delimiter, e.g. '<script'
- * @param $end end delimiter, e.g. '</script>'
- * @return cleaned string, e.g. 'foobar'
+ *
+ * @param string $string Input string, e.g. `foo<script>superscript()</script>bar`
+ * @param string $start Start delimiter, e.g. `<script`
+ * @param string $end End delimiter, e.g. `</script>`
+ * @return string Cleaned string, e.g. `foobar`
+ *
+ * @todo This function can possibly be simplified to use a single `substr` command.
  */
 function stripWithDelimiters($string, $start, $end) {
 	while(strpos($string, $start) !== false) {
@@ -101,10 +175,13 @@ function stripWithDelimiters($string, $start, $end) {
 
 /**
  * Remove HTML sections containing one or more sections using the same HTML tag
- * @param $string input string, e.g. 'foo<div class="ads"><div>ads</div>ads</div>bar'
- * @param $tag_name name of the HTML tag, e.g. 'div'
- * @param $tag_start start of the HTML tag to remove, e.g. '<div class="ads">'
- * @return cleaned string, e.g. 'foobar'
+ *
+ * @param string $string Input string, e.g. `foo<div class="ads"><div>ads</div>ads</div>bar`
+ * @param string $tag_name Name of the HTML tag, e.g. `div`
+ * @param string $tag_start Start of the HTML tag to remove, e.g. `<div class="ads">`
+ * @return string Cleaned String, e.g. `foobar`
+ *
+ * @todo This function needs more documentation to make it maintainable.
  */
 function stripRecursiveHTMLSection($string, $tag_name, $tag_start){
 	$open_tag = '<' . $tag_name;
@@ -131,9 +208,13 @@ function stripRecursiveHTMLSection($string, $tag_name, $tag_start){
 }
 
 /**
- * Convert Markdown tags into HTML tags. Only a subset of the Markdown syntax is implemented.
- * @param $string input string in Markdown format
- * @return output string in HTML format
+ * Convert Markdown into HTML. Only a subset of the Markdown syntax is implemented.
+ *
+ * @link https://daringfireball.net/projects/markdown/ Markdown
+ * @link https://github.github.com/gfm/ GitHub Flavored Markdown Spec
+ *
+ * @param string $string Input string in Markdown format
+ * @return string output string in HTML format
  */
 function markdownToHtml($string) {