SGML makefile

Can I ask why we seem to build the HTML twice in the SGML makefile?

$(addsuffix .tar, $(BOOKS)):
        $(MAKE) -C sgml clean
1)      $(MAKE) -C sgml $(basename $@).html
2)      $(MAKE) -C sgml $(basename $@).html JADEFLAGS='-V html-manifest'
        cd sgml && $(TAR) -cf ../$@ `cat HTML.manifest` `echo *.gif | grep -v '\*'` *.css

I don't understand.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026