Schemas and mixed content with Relax NG and W3C XML Schema

hi,

this is a question about schemas

I know that with DTDs, when a text is allowed with elements, the best we 
can do is to allow it everywhere between other elements that can be 
repeated at any place in the text :

<!ELEMENT p (#PCDATA|a|ul|b|i|em)*>

unfortunately, we can't enforce the text to be at a given place :

<person>Mr <firstname>John</firstname><lastname>Doe</lastname></person>

the following DTD is invalid, but explain what we'd like to have :
<!ELEMENT person (#PCDATA,firstname,lastname)>

I wonder if there are also similar limitations with Relax NG and W3C XML 
Schema and why ?

-- 
Cordialement,

               ///
              (. .)
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|      Philippe Poulard       |
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