An estranged lesbian couple's Supreme Court fight over their seven-year-old daughter is the first case of its kind and raises key issues, a lawyer has said.
Five Supreme Court justices are analysing evidence at a hearing in London following rulings by judges in the High Court and Court of Appeal.
One woman is the youngster's biological mother and sole legal parent - the second woman considers herself a "de facto" parent, courts have heard.
Their relationship broke down in 2011, more than three years after the girl was conceived by IVF treatment and born.
Judges have been told the girl was taken to Pakistan by her biological mother in early 2014.
The second woman had then begun legal action and asked judges to order the youngster's return to the UK.
But a High Court judge and Court of Appeal judges concluded they did not have the "jurisdiction" to make such an order because the girl was not habitually resident in the UK when legal proceedings were launched.
The second woman is now hoping the Supreme Court will rule in her favour.
Solicitor Pauline Fowler, a partner at Hughes Fowler Carruthers, said the hearing is the first of its kind, and added: "This case gives the Supreme Court the opportunity to consider thoroughly a number of issues - the status of gay parents where the non-birth parent has no legal status, what makes an adult a 'psychological parent', the definition of 'habitual residence', and of course the rights and wrongs of a unilateral decision by a gay parent to remove a child from the country."
Supreme Court justices are expected to finish hearing evidence on Wednesday.
They are not expected to deliver a ruling until next year.
Judges have ruled that no-one involved can be identified in reports.
Mrs Justice Hogg initially analysed the case at a hearing in the Family Division of the High Court in 2014 and dismissed an application by the second woman.
A panel of appeal judges - which included Sir James Munby, the head of the Family Division of the High Court - dismissed an appeal by the second woman after a hearing in the Court of Appeal earlier this year.