No special mechanism is provided for notifying input device errors to the application; input devices provide input only. The use of prn_error is applicable to output requests only. If error handling is required for input devices (for example, a magnetic stripe reader might need to be able to inform the application that it had failed to read valid characters from a stripe) the information should be collected by defining a POD whose purpose is to collect information about the input device.
For example, the complete sequence of actions by the application in order to read a magnetic stripe might be as follows:
1 Select a POD defined with parameters that describe the stripe to be read
2 Select the stripe reader as an input source and read from it
3 Send a dummy print to the POD, which will return an error if the stripe was not correctly read