XML tutorial: Inheritance and substitution groups: "xsi:type"
This one correctly explains the difference between xsi:type (Subsumption) and substitutionGroup usage. Many other docs assume (incoreectly?) that blockDefault="substitution" blocks xsi:type usage. This doc suggests blockDefault="all" to disallow xsi:type.
This is Argyn's blog. I comment on topics of my interests such as software, math, finance, and music. Also, I write about local events in Northern Virginia, USA and all things related to Kazakhstan