In previous sections, we have deliberately omitted a lot of
DocBook's history. XML has an older brother,
Standard Generalized Markup Language (SGML).
Until mid-2002, no discussion of DocBook would have been
complete without a long excursion into SGML, the differences between
SGML and XML, and detailed descriptions of the SGML DocBook toolchain.
Life can be simpler now; an XML DocBook toolchain is available in open
source, works as well as the SGML toolchain ever did, and is easier to