code: static String addLessExtendsTo( FormattableContainer container, LessObject obj, String extendSelector ) {
          String baseSelectors = null;
          do {
              int idx1 = extendSelector.indexOf( ":extend(" );
              int idx2 = extendSelector.indexOf( ')', idx1 );
              int idx3 = extendSelector.lastIndexOf( ',', idx1 );
              String selector = extendSelector.substring( idx3 + 1, idx1 ).trim();
              String[] baseSelector = new String[] { selector };
              if( baseSelectors == null ) {
                  baseSelectors = selector;
              } else {
                  baseSelectors = baseSelectors + ',' + selector;
              }
              String params = extendSelector.substring( idx1 + 8, idx2 ).trim();
      
              for( String param : params.split( "," ) ) {
                  boolean all = param.endsWith( " all" );
                  if( all ) {
                      param = param.substring( 0, param.length() - 4 ).trim();
                  }
                  container.add( new LessExtend( obj, baseSelector, param, all ) );
              }
              idx2++;
              if( idx2 < extendSelector.length() ) {
                  while( idx2 < extendSelector.length() ) {
                      char ch = extendSelector.charAt( idx2++ );
                      switch( ch ) {
                          case ',':
                              break;
                          case ' ':
                              continue;
                          default:
                              throw obj.createException("Unrecognized input: '" + extendSelector + "'" );
                      }
                      break;
                  }
                  extendSelector = extendSelector.substring( idx2 ).trim();
                  if( extendSelector.length() > 0 ) {
                      continue;
                  }
              }
              break;
          } while(true);
          return baseSelectors;
      }
docs: Parse the extendSelector,create the needed LessExtend objects and add it to the container.
  
  @param container
  the container that should add the created LessExtend
  @param obj
  another LessObject with parse position.
  @param extendSelector
  the completely selector like "foo:extends(bar all)"
  @return the base selector