user-warning-directive = ( $UWARNING | $UW ) [ condition "," ] message .
Display a user warning message.
<condition>:
An optional boolean expression that conditions the action: if true the warning is treated.
<message>:
A string expression that gives a literal string.
{$IF FREQUENCY < 4000000}
{$UWARNING ’Inaccurate timings will occur at this frequency’}
{$IFEND}
{$UWARNING FREQUENCY < 4000000, ’Inaccurate timings will occur at this frequency’}