For XSL, XSLT and XPath, start with the W3C recommendations at
www.w3.org/TR/xsl,
www.w3.org/TR/xslt
and
www.w3.org/TR/xpath.
This includes a section on FO (formatting objects),
www.w3.org/TR/xsl/slice6.html#fo-section.
Lars Marius Garshol indexes most available XSLT engines at
www.garshol.priv.no/download/xmltools/cat_ix.html#SC_XSLT.
The latest information on tDOM is at
mini.net/tcl/tDOM.
For SAX, see
www.megginson.com/SAX.
Cocoon information starts at
xml.apache.org/cocoon.
Learn more about scripted documents at
mini.net/tcl/ScriptedDocument.
I keep hyperlinks and other information and opinions pertinent to my own XSLT projects at
starbase.neosoft.com/~claird/comp.text.xml/XSLT.html.