the content of element type classes must match (class* parameter*)

Question

I have following issue while creating testNG xml files i have test ng xml files having below lines.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Regression">
    <test thread-count="5" name="Personal Loan">
        <classes>
                <groups>
                <run>
                    <include name="Smoke" />
                </run>
            </groups>
            <class name="test.Day1" />
            <class name="test.Day2" />
            <class name="test.Day3" />
            <class name="test.Day4" />
        </classes>
    </test>
</suite>

for <classes> it is showing error as the content of element type classes must match (class* parameter*) the content of element type classes must match (class* parameter*)

could you please me solve this issue ?