Why XML attributes that are ID must start with a letter?

Question

Firstly, I'd like to have a confirm of that, (XML attributes that are ID must start with a letter). Because I tried to put a date (dd/mm/yyyy) as a ID, but it gives me an error if I don't add a letter at the start. After, is there a way to identify the "date" in the DTD better than "CDATA"?

XML:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE TVchannel SYSTEM "TVchannel.dtd">
<TVchannel>
    <dailyProgrammation date="28/11/2003">
        <programs>
            ...
        </programs>
    </dailyProgrammation>
</TVchannel>

DTD:

<!ELEMENT TVchannel(dailyProgrammation)>
<!ELEMENT dailyProgrammation(programs?)>
<!ATTLIST dailyProgrammation data CDATA #REQUIRED>
...

(Edit) I found useful answers here that explained me many things, however by adding NCName in the .dtd VS Code doesn't recognize it, and in the .xml it says: 'there is [1] error in the .dtd'.

<!ATTLIST dailyProgrammation data ID NCName #REQUIRED>

score 1 · Answer 1 · answered Dec 12 '22 at 11:47

Yes, ID values in XML follow the same rules as element and attribute names, so they have to start with a letter (and can't contain characters such as "/"). The rule makes little sense in a pure XML context, but it was inherited from SGML, where it allowed IDs to be written in contexts other than as attribute values.

Why XML attributes that are ID must start with a letter?

1 Answers1