doc about xml files

hi

is there a doc of the layout of the xml files used by mingw-get ?

for example, what is strange to me is that, in mingw32-zlib.xml for 
example, there are 2 "package" tags:

     <package name="mingw32-zlib" alias="zlib">

and

     <package name="mingw32-libz" alias="libz">

Note that i would like a complete doc, not only an explanation of the 
"package" stuff above.

thank you

Vincent Torri

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