•case-sensitive
•well-formedness
constraints (partial list)
–every element must
have start tag and end tag
–elements must be
correctly nested
–attribute values must
be quoted (matching single or double)
•XML parser checks XML
document to make sure that [1] it is
well-formed (complies with all w.f. constraints in
specification), and [2] it is valid, meaning the
tag names and order conform to the XML
application’s Document Type Definition (DTD)—the
definition of what tags it may have and in
what order