docs: protected File getRelativeFile( File baseDir, File targetFile ) throws IOException
      {
          String baseDirStr = baseDir.getPath();
          String targetDirStr = targetFile.getPath();
          
          if ( targetDirStr.equals( baseDirStr ) )
          {
              return new File( "." );
          }
          else if ( targetDirStr.startsWith( baseDirStr + File.separator ) ) // add slash to ensure directory
          {
              return new File( targetDirStr.substring( baseDirStr.length() + 1 ) ); // + slash char
          }
          
          throw new IOException( "Unable to relativize " + targetDirStr + " to " + baseDir );
      }