Several arguments sustain the jurisdictional choice made by UIFSA. First, "jurisdiction by ambush" will be avoided. That is, personal service on either the custodial or noncustodial party found within the state borders will not yield jurisdiction to modify. Thus, a parent seeking to exercise rights of visitation, delivering or picking-up the child for such visitation, or engaging in unrelated business activity in the State, will not be involuntarily subjected to protracted litigation in an inconvenient forum. The rule avoids the possible chilling effect on the exercise of parental contact with the child that the possibility of such litigation might have. Second, almost all disputes about whether the tribunal has jurisdiction will be eliminated; submission by the petitioner to the State of residence of the respondent alleviates this issue completely. Finally, because there is an existing order the primary focus will shift to enforcement, thereby curtailing to a degree unnecessary, time-consuming modification efforts. The array of enforcement procedures available administratively to support enforcement agencies may be invoked without resort to action by a tribunal, which had constituted a bottleneck under RURESA and URESA.

There are two exceptions to the rule of Subsection (a)(1) requiring the petitioner to be a nonresident of the forum in which modification is sought. First, under Subsection (a)(2) the parties may agree that a particular forum may serve to modify the order. Second, Section 613, infra, applies if all parties have left the original issuing State and now reside in the same new forum State. Subsection (a)(2), which authorizes the parties to terminate the continuing, exclusive jurisdiction of the issuing State by agreement, is based on several implicit assumptions. First, the subsection applies even if the issuing tribunal has continuing, exclusive jurisdiction because one of the parties or the child continues to reside in that State. Subsection (a)(2)