This information is in large part from the Uniform Law Commission's website, with my edits and additions. The remarks under Comments are mine.
In 1968, the Uniform Law Commissioners promulgated the Uniform Child Custody Jurisdiction Act (UCCJA). The UCCJA was designed to discourage interstate kidnapping of children by their non-custodial parents. Before the UCCJA, it was a common practice for non-custodial parents to take children across state lines. They hoped to find sympathetic courts willing to reverse unfavorable custody orders. In too many cases, they were successful. All the states adopted the Act.
The way they did it is to define jurisdiction for interstate cases based on where the child lives and protect that jurisdiction and orders made by that state from being modified by another state without a change in circumstances that warrants it.
In 1998, the Commissioners promulgated the uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA).
The UCCJEA provides for continuing exclusive jurisdiction. If a state once takes jurisdiction over a child custody dispute, it retains jurisdiction so long as that state, by its own determination, maintains a significant connection with the disputants or until all disputants have moved away from that state. [
The UCCJEA provides for temporary emergency jurisdiction, that can ripen into continuing jurisdiction only if no other state with grounds for continuing jurisdiction can be found or, if found, declines to take jurisdiction. The child’s presence and its abandonment, mistreatment or abuse still trigger the taking of emergency jurisdiction, but threats to siblings or a parent also can trigger the taking of emergency jurisdiction. Because of the priority given to the home state of the child, the home state will most often be the state from which continuing jurisdiction is exercised.
Priority for home state jurisdiction, continuing exclusive jurisdiction and temporary emergency jurisdiction mean that orders made pursuant to the UCCJEA will have the full weight of the Full Faith and Credit Clause of the U.S. Constitution behind them.
The UCCJEA also adds enforcement provisions to the jurisdictional provisions. The UCCJEA requires a state to enforce a custody or visitation order from another state that conforms substantially with this Act. An order from a state that has continuing exclusive jurisdiction, therefore, will surely be enforced.
One enforcement procedure is to register the out-of-state order. If the registration is not contested, the registered order may be enforced by any means available to enforce a domestic order. This would ordinarily mean using the contempt powers of the court to assure that the custody or visitation order is honored by the parent subject to it.
There is an expedited remedy, however, that also is available. Upon receiving a verified petition, the court orders the party with the child to submit to an immediate hearing (the next judicial day unless impossible) for enforcement. The court may rule with respect to enforcement at the hearing, although there are provisions to allow for extended hearing and standards to contest enforcement. This remedy operates much like habeas corpus, in which the body subject to the writ must be presented immediately to the court.
If there is danger to a child or if it appears that the child will be removed from the enforcing jurisdiction, a petition may also be filed for a warrant to take physical custody of the child along with a petition for an expedited proceeding. If the warrant issues, law enforcement officers will serve the warrant and obtain physical custody of the child.
As a last enforcement device, the UCCJEA gives prosecutors the power to enforce custody or visitation orders, and law enforcement officers the power to locate a child under instructions from prosecutors. These powers give parents and others who are the victims (along with children) of parental kidnapping the ability to seek help from those who enforce the criminal law. The effect is to provide a complete group of effective remedies.
The UCCJEA provides a remarkable statutory method to obtain relief both in California and in other states. As it adds enforcement to what had been the law under the UCCJA, orders made can be enforced where previously they could not. There are tools for relief. An example would be where a parent takes a child to another state without the permission of the other parent. A court in that state can decline jurisdiction on the ground of unjustifiable conduct. Another example: the non-custodial parent believes there is cause for the court to assert temporary emergency jurisdiction to protect a child and the child is present in the state, that state's court can make such an order. There is a provision enabling courts to contact courts in another state which can result in a joint hearing with the parties and both courts participating. So there are now tools to enable a parent to seek and succeed in obtaining the return of a child.