code: public static function joinPath( $base, $path ) {
  		if ( substr( $path, 0, 1 ) === '/' ) {
  			// $path is absolute.
  			return $path;
  		}
  
  		if ( substr( $base, 0, 1 ) !== '/' ) {
  			// $base is relative.
  			return false;
  		}
  
  		$pathParts = self::splitPath( $path );
  		$resultParts = self::splitPath( $base );
  
  		while ( ( $part = array_shift( $pathParts ) ) !== null ) {
  			switch ( $part ) {
  			case '.':
  				break;
  			case '..':
  				if ( count( $resultParts ) > 1 ) {
  					array_pop( $resultParts );
  				}
  				break;
  			default:
  				$resultParts[] = $part;
  				break;
  			}
  		}
  
  		return implode( '/', $resultParts );
  	}
docs: Join path components.
  
  @param string $base Base path.
  @param string $path File path to join to base path.
  @return string