Javascript: using xml id attributes to getElementById

I’m trying to get getElementById to work with an XML structure. In this case, I am creating web pages based on two xml files: positions and personnel. I create a logical link between them by using a modified “person’s name” (with bl
anks replaced by underscores and apostrophes & periods removed) as the incumbent in the position file. The same thing is set as an id attribute in the personnel file.

The dtd for the personnel file is:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE people [
   <!ELEMENT person (name, email?, bio, telephone*)>
        <!ATTLIST person id ID #REQUIRED > 
        <!ELEMENT name              (#PCDATA)>
        <!ELEMENT email (email-name, email-domain)>
            <!ELEMENT email-name    (#PCDATA)>
            <!ELEMENT email-domain  (#PCDATA)>
        <!ELEMENT bio (photo, p*, li*)>
            <!ELEMENT photo         (#PCDATA)>
            <!ELEMENT p             (#PCDATA)>
            <!ELEMENT li            (#PCDATA)>
        <!ELEMENT telephone (tel-type, tel-area, tel-num, tel-ext?)>
            <!ELEMENT tel-type      (#PCDATA)>
            <!ELEMENT tel-area      (#PCDATA)>
            <!ELEMENT tel-num       (#PCDATA)>
            <!ELEMENT tel-ext       (#PCDATA)>
 ]>

The data gets loaded into peopleList but

var incumbentDetails = peopleList.getElementById(curIncumbent);

fails. I’ve verified that curIncumbent contains the correct (and valid) information and checked for duplicate ids (there aren’t any). I’ve verified that I’ve loaded the correct number of “person” elements.

What I haven’t found in my searching is a sample DTD that actually shows an ID attribute in a full defined DTD. I suspect the issue may be in the DTD but it’s hard to tell if I’m making progress when the function only fails.

Any help would be appreciated.