Limitations of Joost:

dynamically generated names for elements, attributes, and PIs are not 
checked for XML correctness

STXPath Lexer accepts only ASCII characters within identifiers

stx:process-document
- if href evaluates to a node then the base of the *current* input stream
  is used, not the base of the node. This will give different results only
  if the node comes from another document with a different base URI, i.e.
  the node must have been stored in a variable.

stx:result-document
- no check for multiple openings of the same file (leads to invalid contents)
