Creating a DTD

I'm working on a DTD for an EDI message in XML. But some of the element definitions confuse me.

I know that the following...

<!ELEMENT ElementName (#PCDATA)>

means that the Element with the name ElementName cannot be empty ans should contain parsed character data (text).

I also know that the following...

<!ELEMENT ElementName EMPTY>

meanse that the element with the name ElementName may be empty and omitting from the XML document.

Anyone can rectify me on this if I'm wrong (I'm a newbie to XML).

But the parts that confuse me is...

<!ELEMENT ElementName ANY>

and

<!ELEMENT ElementName %;>

Can anyone explain this to me and the other XML Schema newbies?

I'm not sure what you mean. An EMPTY declaration means the element must be empty. That is, your DTD above means that the element must appear as <ElementName /> or <ElementName></ElementName>.

Elements declared with the ANY keyword, can literally contain anything. They can be empty, contain PCDATA, or other elements. There is no restriction.

When you encounter a %xxx; sequence, that's an entity. Entities must be previously defined in the DTD. For example,

Is the same as saying,

Entities are useful when you have groups of similar elements/attributes/whatever, that are commonly shared between multiple elements.