as "an elusive term, meaning that the defendant knows his rights, the nature of the charge to which he is pleading, and the consequences of his plea." "Voluntary" has been described as also "an elusive term which has come to mean not induced by 'improper' inducements, such as bribing or physical violence, but not including the inducements normally associated with charge and sentence bargaining (except for inducements involving 'overcharging' by prosecutors)." Empirical research has demonstrated that violent conditions in jails during pretrial detention of people who are legally innocent do improperly induce or coerce guilty pleas, but this has not constitutionally invalidated the pleas under current Supreme Court precedent. Virtually all jurisdictions hold that defense counsel need not discuss with defendants the collateral consequences of pleading guilty, such as consecutive sentencing or even treatment as an aggravating circumstance in an ongoing capital prosecution. However, the Supreme Court recognized an important exception in Padilla v. Kentucky (2010), in which the Court held that defense counsel is obligated to inform defendants of the potential immigration consequences of a guilty plea. Thus a defendant who is not advised of immigration consequences may have an ineffective assistance of counsel argument. In the U.S. federal system, the court must also satisfy itself that there is a factual basis for the guilty plea. However, this safeguard may not be very effective because the parties, having reached a plea agreement, may be reluctant to reveal any information that could disturb the agreement. When a plea agreement has been made, the judge's factual basis inquiry is usually perfunctory, and the standard for finding that the plea is factually based is very low. Special pleas Other special pleas used in criminal cases include the plea of mental incompetence, challenging the jurisdiction of the court over the defendant's person, the plea in bar, attacking the jurisdiction of the court over the crime charged, and the plea in abatement, which is used to address procedural errors in bringing the charges against the defendant, not apparent on the "face" of the indictment or other charging instrument. Special pleas in federal criminal cases have been abolished, and defenses formerly raised by special pleas are now raised by motion to dismiss. A conditional plea is one where the defendant pleads guilty to the offense but expressly reserves the right to appeal certain aspects of the charges (for example, that the evidence was illegally obtained).