Question about validation xml with xsd

Hi,
I want to apologize in advance for my bad english.

I want to validate xml(1), which is as follows:

*<letter>
Hi <name>Milena</name>,
You have <count>1</count> unpaid bill.
</letter>*


The xsd must be:

*<xsd:element name="letter">
 <xsd:complexType mixed="true">
   <xsd:sequence>
     <xsd:element name="name" type="xsd:string"/>
     <xsd:element name="count" type="xsd:integer"/>
   </xsd:sequence>
 </xsd:complexType>
</xsd:element>*

But If I have that xml(2):

*<letter>
Hi <name>Milena</name>,
You have to give me <count>1</count> apple.
</letter>*

and If I try to validate this xml with the given xsd, the result will be
also OK.
I want to restrict character data in mixed content.
And If I have xml(2)  instead of xml(1), I want to know that.

My question is: How to write my xsd, so that validation of second xml to be
ERROR?


Thank you in advance.
Have a nice day!

--
Milena