As of 8/3017, there is a new variable in Participants coding called Prisoner. This dummy variable indicates whether the appellant was a prisoner in a state or federal prison and was challenging something about the conditions in prison (e.g., civil rights, liberties, etc.) and/or was bringing a habeas petition. This is NOT the same as an appeal by a (convicted) criminal defendant.
Note that some cases have been automatically coded as Prisoner = 1, but should be verified by human coders to ensure that these are not actually criminal cases.