Availability in versions: `PHP 4.0.4`
|Parameter||Data type||Default value||Note|
||not||The constant name.|
The filter() method must return one of three values upon completion.
Filter processed successfully with data available in the
|PSFS_FEED_ME||Filter processed successfully, however no data was available to return. More data is required from the stream or prior filter.|
|PSFS_ERR_FATAL (default)||The filter experienced an unrecoverable error and cannot continue.|