Is Visible hook
Use this hook to remove custom form commands from the session.
This hook should not use actual values of the form fields. The code in the hook
is processed before actual data is read from the database or the form. To control
the availability of the form command that is based on data on the screen, you can
use the Is Enabled
hook. You can use data that is
not related to actual contents of the screen, for example parameter data.
See this example:
function extern boolean function.publish.item.is.visible()
{
|* Publishing only available for production companies
return(get.compnr() >= 0100 and get.compnr() < 1000)
}