https://chrome.google.com/webstore/detail/dynalist-allstar/kljpaieidlmmnigjigfbmfbhabolpkbl?hl=en
Right click on a document in File pane and select "Open in Side" option to open 2nd document in same window.
You can work on both the documents at same time and Dynalist will save the changes.
To disable/enable this feature go to Menu -> Allstar Settings option.