code: protected static function is_modified_file( $filepath ) {
  
  		$actual = filemtime( $filepath );
  
  		$last = isset( self::$files[ $filepath ] ) ? self::$files[ $filepath ] : 0;
  
  		if ( $actual !== $last ) {
  
  			self::$files[ $filepath ] = $actual;
  
  			self::$changes = true;
  
  			return self::$changes;
  		}
  
  		return false;
  	}
docs: Check if the file was modified.
  
  @since 1.0.4
  
  @param string $filepath → path of the file.
  
  @return boolean