DTD validation error with libxml2

Question

I try to validate some xml data with a dtd. For that I have to use libxml2. The produced xml data looks like this:

    <?xml version="1.0"?>
        <root>
            <vent id="1">
                <usb_device_id>1</usb_device_id>
                <usb_device_channel>2</usb_device_channel>
                <vent_box_id>3</vent_box_id>
                <vent_box_channel>4</vent_box_channel>
            </vent>
       </root>

My dtd looks like this:

    <!ELEMENT root (vent) >
    <!ELEMENT vent (usb_device_id, usb_channel, vent_box_id, vent_box_channel) >
    <!ATTLIST vent id (ID) #REQUIRED >
    <!ELEMENT usb_device_id (CDATA) >
    <!ELEMENT usb_channel (CDATA) >
    <!ELEMENT vent_box_id (CDATA) >

I use http://xmlsoft.org/html/libxml-valid.html#xmlValidateDtd on the parsed tree. With this setup I get the error message:

element vent: validity error : Value "1" for attribute id of vent is not among the enumerated set

Where I am wrong? Thanks in advance...

Answer 1

Your attribute id is defined as having the type ID . That means it has to be a valid XML name and thus its first character must not be a digit but a letter. A description can be found here or even better in the W3C documentation itself: ID and Names (copied form BLUEPIXY's comment)