As Paper is improving towards a powerful collaboration tool, I would like to see this features in near future. For sceintific and academic writing, citation is an essential feature. It would be nice if Paper adopts to one of the most popular citation format BibTex. What paper need to implement is someting like this: in the text we need a citation field, say, "\cite{tag_journal_1}". And in the end of the text include the list of citaion with tag.
\begin{Bibliography}[Bibliography Style]
@tag_journal_1{
Author: author one, author two,
Title: This is Title,
Journal: Journal Name,
Vol: xx,
Pages: xxx
Year: 2018}
\end{Bibliography}
Good thing is that bibliography can be downloaded from most journals as above BibTex format, it is widely popular. Even better if Paper implements an universal citation manager where we can directly import citations, and insert into any Paper document.