What is it mean by BUILDING DocBook ?

Hi devs,

I'm Gihan Chanuka. An 
undergraduate of Bsc Engineering, University of Moratuwa, Sri Lanka. I'm
 new to open source and also to DocBook. But as I see, DocBook is one of
 the interesting and innovative idea.  So, I liked to get familiar with 
the DocBook project.

I went through some of the tutorials and documentation about it. And
 then, transformed a small DocBook document to html using xsltproc to 
understand how it works.

I got the DocBook source code by using SVN and went though "trunk>xsl>ReadMe.BUILD" and follow the steps in that file.

Can you tell me what is meant by "building" DocBook? It use XSL 
language to interpret and virtual processor called "XSLT" to transform 
the xml files. Since, we don't need to XSLs, what exactly we do when 
building?

Thanks in advance!

-- 

-- 
~ Gihan Chanuka
~ Undergraduate of Bsc Engineering,
~ Department of Computer Science and Engineering,

~ University of Moratuwa,

~ Sri Lanka.