Is Valid hook

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

Example:

function extern boolean tcibd001.cdf_colr.is.valid(long mode)
{
        select  txcom002.colr 
        from    txcom002
        where   txcom002.colr = :tcibd001.cdf_colr
        as set with 1 rows
        selectdo
                return(true)
        endselect
        dal.set.error.message("txcomt002", tcibd001.cdf_colr)
        |* Color %1$s not found
        return(false) 
}