code: protected void check (File source, String mname, int mline, String fname, int fline)
          throws IOException
      {
          if (mline == -1 && fline != -1) {
              throw new IOException(
                  "Found " + fname + " marker (at line " + (fline+1) + ") but no " + mname +
                  " marker in '" + source + "'.");
          }
      }
docs: Helper function for sanity checking marker existence.