What sound did the Glagolitic letter pe write, and is it a letter of the alphabet or a variant of another sign?

Why it is open. The letter is encoded in the Unicode Standard and appears in the abecedaria, the alphabet lists copied out as exercises or inscriptions, more often than in running text. The reference literature reads it as a form of p without establishing what distinguished it from the ordinary letter for that sound, and different sources place different numeral values in this part of the order. Nobody holds a position on the question, which is why the atlas records the letter with no numeral value rather than choosing among the values on offer. It is an unfilled gap and not an argument between camps.

What would resolve it. An attestation of the sign in running text, in a context where the word it writes can be identified, would settle the sound. A survey of every surviving Glagolitic abecedary, recording where this sign falls in the order and whether it is ever given a numeral value in the list, would settle whether it was counted as a letter of the alphabet or carried as a variant.

Field. Slavic palaeography; codicology; Old Church Slavonic philology