🚀 go-pugleaf

I have a twofold request to comp.text readers with SGML experience:

1.  Could someone point me to a document that defines what SGML is and how to
    use it?

2.  Could someone post a real brief summary of the SGML spec--perhaps just a
    list of the tags?

I know nothing about SGML, but am interested in using it for the sake of
employing a more universal concept of tagging.  We currently use both Eroff
and FrameMaker.  Do either of these packages lend themselve well to SGML?

etan