Brașov Charter

Ivan Sratsimir signs himself here "Иванъ Срацимиръ Царъ владеющи" — Ivan Sratsimir, ruling tsar. The charter is the primary evidence for how the ruler of Vidin styled himself in an official act of his own chancery, as opposed to how flatterers styled him.

That matters because Vidin is the rare case of an appanage becoming a fully independent political unit. His brother Ivan Shishman signed as tsar and autocrat of all Bulgarians and Greeks, but the difference is traditional formula, not constitutional standing: internationally the two were treated as equals, and the Patriarch of Constantinople addressed them as such.