Is Valid hook

Use this hook to perform any checks not already defined in one of the other field hooks.

Example:

function extern boolean tdsls401.item.is.valid(long mode)
{
        if not txexpdll0001.item.allowed(tdsls401.ofbp, tdsls401.item) then
                dal.set.error.message(
                      "@Item not allowed for this business partner”)
                return(false)
        endif
        return(true)
}