What do you think the following DTD snippet would imply?

	<!ELEMENT CONTACT (NAME, EMAIL+)>
	<!ELEMENT NAME (#PCDATA)>
	<!ELEMENT EMAIL (#PCDATA)>

Take a look at the regular expression character chart above and guess. That is right! It would mean that a CONTACT element could have a NAME element followed by one or more EMAIL elements. Thus, the following XML would be valid

        <CONTACT>
        <NAME>Jim Sanger</NAME>
        <EMAIL>sanger@sanger.com</EMAIL>
        <EMAIL>sanger@yahoo.com</EMAIL>
        <EMAIL>sanger@netscape.com</EMAIL>
        </CONTACT>

What about the following?

        <CONTACT>
        <NAME>Jim Sanger</NAME>
        </CONTACT>

Well that would be invalid because the "+" sign specifies "one or more". To allow for "zero or more" occurrences, you must use a "*" such as

	<!ELEMENT CONTACT (NAME, EMAIL*)>
	<!ELEMENT NAME (#PCDATA)>
	<!ELEMENT EMAIL (#PCDATA)>