Data length validations using DTD

How do I do the data length validations in DTD?

I want to restrict an element length using DTD. I was given only the DTD and 
not the schema by our client and
they provided the doc with length restrictions.

DTD contains elements like the following:

<!ELEMENT myelement (#PCDATA)>

<!ELEMENT ShipTo (myelement)>

But "myelement" length should be restricted to 100 char. How can I achieve 
this?

Thank you.

Sudheshna

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