restrict the value of one child based on value from another child

[leon]

Hi all,

a question for you:

suppose i have an element of complex type which contains two child elements (both of child elements
are simple types, say an integer for example's sake)

suppose i then want to restrict the value of one child element to be no greater than the other child
element...

<parent>
<childOne>57</childOne>
<childTwo>7</childTwo>
</parent>

From the aforementioned example, I want to make sure that whatever the value in childOne - childTwo
will NOT have the value greater (e.g. in this case no greater than 57)

kind regards,
Leon.