code: private void bracketProcessBoundary(BracketData bd, int lastCcPos,
                                          byte contextLevel, byte embeddingLevel) {
          IsoRun pLastIsoRun = bd.isoRuns[bd.isoRunLast];
          if ((DirPropFlag(dirProps[lastCcPos]) & MASK_ISO) != 0) /* after an isolate */
              return;
          if (NoOverride(embeddingLevel) > NoOverride(contextLevel))  /* not a PDF */
              contextLevel = embeddingLevel;
          pLastIsoRun.limit = pLastIsoRun.start;
          pLastIsoRun.level = embeddingLevel;
          pLastIsoRun.lastStrong = pLastIsoRun.lastBase = pLastIsoRun.contextDir = (byte)(contextLevel & 1);
          pLastIsoRun.contextPos = lastCcPos;
      }
docs: /* LRE, LRO, RLE, RLO, PDF