I see the ZVON.org site has recently been renovated. It is a great site with tutorials or reference material on dozens of Web-related topics. Highly recommended.
The site slogan is ZVON.org cleaning information pipelines but the logo says ZVON the information plunger which has me chuckling.
One of the reasons for the quick success of Schematron in its first year (1999-2000) was that Czech academic Dr Miloslav Nic put up a great little tutorial on his ZVON site. The new site has good preamble material on Schematron so far: I hope in due time the Schematron tutorial will make an updated comeback.