Type ID in DTD

[Ravikiran Muvva]

Hi,
This is a sample question in XML 141 sample test.Can anyone explain me why a,d are the correct answers for this??
Which of the following would raise an error if the empID attribute's data type was defined as type ID in the DTD?
a) <name empID="17563">Joe Smith</name>
b) <name empID="ft:17563">Joe Smith</name>
c) <name empID="a17563">Joe Smith</name>
d) <name empID="">Joe Smith</name>

Thanks in advance
rkmuvva

[Valentin Crettaz]

Attributes defined as ID must contain only characters allowed for NMTOKEN (letters, digits, point [ . ] , hyphen [ - ], underline [ _ ] and colon [ : ] ) and must start with a letter.
b and c satisfy to this rule whereas a and d don't.
For more details, please consult
Zvon.org DTD tutorial
W3C XML specification

[Madhav Lakkapragada]

Attributes defined as ID must contain only characters allowed for NMTOKEN (letters, digits, point [ . ] , hyphen [ - ], underline [ _ ] and colon [ : ] ) and must start with a letter.
On the same rule, has anyone heard of Processors/Parsers giving errors because the ID value has a "." (period) in the value. Acc. to this rule, it seems to be valid.
- madhav