public static function key(array $data) {
		$data += [
			'fields' => [],
			'locked' => [],
			'excluded' => []
		];
		return static::_compile(
			array_keys(Set::flatten($data['fields'])),
			$data['locked'],
			array_keys($data['excluded'])
		);
	}
public static function key(array $data) {
		$data += [
			'fields' => [],
			'locked' => [],
			'excluded' => []
		];
		return static::_compile(
			array_keys(Set::flatten($data['fields'])),
			$data['locked'],
			array_keys($data['excluded'])
		);
	}
public static function key ( array $ data ) { $ data += [ 'fields' => [ ] , 'locked' => [ ] , 'excluded' => [ ] ] ; return static :: _compile ( array_keys ( Set :: flatten ( $ data [ 'fields' ] ) ) , $ data [ 'locked' ] , array_keys ( $ data [ 'excluded' ] ) ) ; }
Generates form signature string from form data.

@param array $data An array of fields, locked fields and excluded fields.
@return string The form signature string.
Generates form signature string from form data .