RE: Is an XPath processor responsible for catching mi

You haven't shown the full context of your stylesheet/xpath expression.

The processor can't assume that because an element is named Book that it
will be a valid instance of the global element declaration Book in the
schema. It might for example be a temporary unvalidated element, and it's
perfectly legitimate to mix validated/valid trees and unvalidated/invalid
trees in the same program.

The XQuery/XPath formal semantics define an optional feature called "static
typing" that guarantees that if the type of $b is known to be
schema-element(Book), then $b/autr is a static type error. But static typing
unfortunately can reject many perfectly reasonable expressions as well, so
many products including Saxon choose not to implement it.

Saxon will give you a compile time warning for this situation. However, if
there is no static type information available, then it can't do this. To get
maximum benefit from schema-aware processing, you should declare the types
of your variables and function parameters (and especially, the type of the
principal input). 

> 
> QUESTIONS
> 
> 1. Is it the responsibility of a schema-aware processor to 
> catch misspelled tag names in XPath expressions?

Yes, provided (a) the type of the context of the path is known, and (b) the
processor implements static typing.
> 
> 2. Is there a flag that I can set in SAXON to tell it to 
> catch such misspelling errors?

You should declare the types of your variables and parameters as accurately
as you can.

The scope for this in freestanding XPath with Saxon is limited; if you want
this it's probably best to process your XPath expressions with the XQuery
processor.

Michael Kay
http://www.saxonica.com/