no mapped file can be loaded, or the
	 * name of the mapped file that was loaded.
	 */
	protected function loadMappedFile($prefix, $relative_class)
	{
		// are there any base directories for this namespace prefix?
		if (isset($this->prefixes[$prefix]) === false) {
			return false;
		}
		// look through base directories for this namespace prefix
		foreach ($this->prefixes[$prefix] as $base_dir) {
			// replace the namespace prefix with the base directory,
			// replace namespace separators with directory separators
			// in the relative class name, append with .php
			$file = $base_dir
				. str_replace('\\', '/', $relative_class)
				. '.php';
			// if the mapped file exists, require it
			if ($this->requireFile($file)) {
				// yes, we're done
				return $file;
			}
		}
		// never found it
		return false;
	}
	/**
	 * If a file exists, require it from the file system.
	 *
	 * @param string $file The file to require.
	 * @return bool True if the file exists, false if not.
	 */
	protected function requireFile($file)
	{
		if (file_exists($file)) {
			require $file;
			return true;
		}
		return false;
	}
}