return $a[$key];
			}

		return null;
	}



	/**
	 * Returns string value
	 */
	public function get_string( $key, $default = '', $trim = true ) {
		$value = (string)$this->get( $key, $default );

		return $trim ? trim( $value ) : $value;
	}



	/**
	 * Returns integer value
	 */
	public function get_integer( $key, $default = 0 ) {
		return (integer)$this->get( $key, $default );
	}



	/**
	 * Returns boolean value
	 */
	public function get_boolean( $key, $default = false ) {
		return (boolean)$this->get( $key, $default );
	}



	/**
	 * Returns array value
	 */
	public function get_array( $key, $default = array() ) {
		return (array)$this->get( $key, $default );
	}



	/**
	 * Returns config value with ability to hook it.
	 * Should be called only when filters already loaded and
	 * call doesn't repeat too many times
	 */
	public function getf( $key, $default = null ) {
		$v = $this->get( $key, $default );
		return apply_filters( 'w3tc_config_item_' . $key, $v );
	}

	/**
	 * Returns string value with ability to hook it
	 */
	public function getf_string( $key, $default = '', $trim = true ) {
		$value = (string)$this->getf( $key, $default );

		return $trim ? trim( $value ) : $value;
	}

	/**
	 * Returns integer value with ability to hook it
	 */
	public function getf_integer( $key, $default = 0 ) {
		return (integer)$this->getf( $key, $default );
	}



	/**
	 * Returns boolean value ability to hook it
	 */
	public function getf_boolean( $key, $default = false ) {
		return (boolean)$this->getf( $key, $default );
	}



	/**
	 * Returns array value ability to hook it
	 */
	public function getf_array( $key, $default = array() ) {
		return (array)$this->getf( $key, $default );
	}



	/**
	 * Check if an extension is active
	 */
	public function is_extension_active( $extension ) {
		$extensions = $this->get_array( 'extensions.active' );
		return isset( $extensions[$extension] );
	}



	public function is_extension_active_frontend( $extension ) {
		$extensions = $this->get_array( 'extensions.active_frontend' );
		return isset( $extensions[$extension] );
	}



	public function set_extension_active_frontend( $extension,
		$is_active_frontend ) {
		$a = $this->get_array( 'extensions.active_frontend' );
		if ( !$is_active_frontend ) {
			unset( $a[$extension] );
		} else {
			$a[$extension] = '*';
		}

		$this->set( 'extensions.active_frontend', $a );
	}



	public function set_extension_active_dropin( $extension,
		$is_active_dropin ) {
		$a = $this->get_array( 'extensions.active_dropin' );
		if ( !$is_active_dropin ) {
			unset( $a[$extension] );
		} else {
			$a[$extension] = '*';
		}

		$this->set( 'extensions.active_dropin', $a );
	}



	/**
	 * Sets config value.
	 * Method to override
	 */
	public function set( $key, $value ) {
		if ( !is_array( $key ) ) {
			$this->_data[$key] = $value;
		} else {
			// set extension's key
			$key0 = $key[0];
			$key1 = $key[1];

			if ( !isset( $this->_data[$key0] ) || !is_array( $this->_data[$key0] ) )
				$this->_data[$key0] = array();

			$this->_data[$key0][$key1] = $value;
		}

		return $value;
	}



	/**
	 * Check if we are in preview mode
	 */
	public function is_preview() {
		return $this->_preview;
	}



	/**
	 * Returns true if we edit master config
	 */
	public function is_master() {
		return $this->_is_master;
	}



	public function is_compiled() {
		return $this->_compiled;
	}



	/**
	 * Sets default values
	 */
	public function set_defaults() {
		$c = new ConfigCompiler( $this->_blog_id, $this->_preview );
		$this->_data = $c->get_data();
	}



	/**
	 * Saves modified config
	 */
	public function save() {
		if ( function_exists( 'do_action' ) )
			do_action( 'w3tc_config_save', $this );

		$c = new ConfigCompiler( $this->_blog_id, $this->_preview );
		$c->apply_data( $this->_data );
		$c->save();
	}



	public function is_sealed( $key ) {
		if ( $this->is_master() )
			return false;

		// better to use master config data here, but
		// its faster and preciese enough for UI
		return ConfigCompiler::child_key_sealed( $key, $this->_data,
			$this->_data );
	}



	/**
	 * Exports config content
	 */
	public function export() {
		if ( defined( 'JSON_PRETTY_PRINT' ) )
			$content = json_encode( $this->_data, JSON_PRETTY_PRINT );
		else
			$content = json_encode( $this->_data );

		return $content;
	}



	/**
	 * Imports config content
	 */
	public function import( $filename ) {
		if ( file_exists( $filename ) && is_readable( $filename ) ) {
			$content = file_get_contents( $filename );
			if ( substr( $content, 0, 14 ) == '