An apparent limitation of iOS is that you cannot open two instances of the same app side by side (with few exceptions, as Safari, Scrivener and Notability).
Notebooks is an amazing app which allows to edit two text documents (or two instances of the same document) side by side on iOS. It even works with PDFs.
This is great for research and comparation purposes. Furthermore there is a Mac version and syncronization through Dropbox is supported.
It has some URL schemes support and also supports TextExpander.
I am sharing a basic Drafts’ action to send a draft to Notebooks.
I think further automation around this app would be great for academics, lawyers and other professionals.