we can create multiple files in a single instance of TextEdit using tab feature. But we can't open multiple files in a single instance. (for example I want to open 4 files together, It open but with 4 different TextEdit window "Image-2")
so switching from one file to another file is difficult.
Issue: Unable to open multiple files together in TextEdit.
Suggestion/Request: we should be able to open multiple files together in TextEdit.
Please see the attached screenshot (image-1) from "Sublime text" file where we can open multiple files together. and (image-2) when we try to open multiple file with "TextEdit".
Image-1
Image-2
This isn't really a developer or API question, so you maybe should ask over at support.apple.com for further insights. However, you should be able to merge multiple app document windows into a single tabbed window by using the standard menu item Window -> Merge All Windows. You should also be able to set tabs as a system-wide default (System Settings -> Desktop & Dock -> Windows -> Prefer tabs when opening applications: Always).