By DANICA KIRKA ,  Associated Press

LONDON (AP) — A unique copy of the U.S. Declaration of Independence has been discovered in an unexpected place - England.
The copy, similar to the one viewed by millions each year at the National Archives in Washington has been locked away in a local records office in southeastern England forgotten by historians. Its significance wasn't understood until recently, when Harvard researcher Emily Sneff stumbled on a mention in a catalog of the office's holdings. Something tickled her curiosity: the copy was written on parchment.
And when Sneff and Harvard professor Danielle Allen saw the document, they were stunned.
"I thought, 'Holy history, Batman!" Allen told The Associated Press on Monday. "We'd seen a lot of copies, but nothing like this."
Sneff and Allen's sleuthing led to a discovery that could shed new light on the founding document of the United States.
The team studied the document for two years and viewed it in person before sharing their conclusions with other historians last week.
The experts have dated what is now being called the "Sussex Declaration" to the 1780s — a time of political tumult before the Constitutional Convention, when the new nation was struggling to survive as a loose association of states governed by the Articles of Confederation.
The document is 24-inches-by-30 inches — the same size as the one housed at the National Archives. Also like the one at the archives, it is written by hand on parchment — the only two of their kind known to exist.
But there are also key differences. The names are not in the same order. For instance, John Hancock isn't listed first or writ large, and the signatories aren't grouped by state.
Historians believe the Sussex Declaration could have been owned by the Third Duke of Richmond, known as the "Radical Duke" because of his support for the American Revolution. The parchment came into the possession of a local lawyer who represented the family. It was deposited at the West Sussex Records Office in the 1950s.
But it remains unclear how the document got to Britain.
The researchers from the Declaration Resources Project plan to test the document this summer in an effort to clarify its provenance, and perform hyper-spectral imaging in hopes of deciphering text at the top of the parchment that appears to have been scraped off.
What is already clear is that the document was made during the tumultuous years after the American Revolution. Just after the signing of the declaration, copies were reproduced and distributed throughout the colonies and across the Atlantic to England. But the Sussex version was created a decade later and based on the original at the National Archives.
The Sussex Declaration is important because it underscores the arguments that divided the revolutionaries as they moved to establish a country. Historians have long debated whether there was continuity between the declaration and the Constitution or if it was a sharp break. The Sussex parchment suggests continuity. But it also has great import to the general public, Allen said.
One of the major debates of the time was whether the new nation would be based on the authority of the people or the authority of the states. The transcriber meticulously copied the declaration only to jumble the signatories as a political statement, giving weight to the people rather than the states, Allen said.
"This is really a symbolic way of saying we are all one people," she said.
It goes to the essence of debates that continue in the U.S., as typified by the fact that Hillary Clinton won last year's popular vote but Donald Trump became president because he won the Electoral College, which ensures the president is elected by a tally of states.
"This manuscript beautifully illuminates the nature of that puzzle," Allen said.