code: public InputStream openStream( URL baseURL, String urlStr, String relativeUrlStr ) throws IOException {
          URL url = new URL( baseURL, urlStr );
          try {
              return openStream( url );
          } catch( Exception e ) {
              // try rewrite location independent of option "rewrite-urls" for backward compatibility, this is not 100% compatible with Less CSS
              url = new URL( new URL( baseURL, relativeUrlStr ), urlStr );
              return openStream( url );
          }
      }
docs: Open an InputStream for the given URL. This is used for inlining images via data-uri.
  
  @param baseURL
  the URL of the top less file
  @param urlStr
  the absolute or relative URL that should be open
  @param relativeUrlStr
  relative URL of the less script
  @return the stream, never null
  @throws IOException
  If any I/O error occur on reading the URL.