Your request is a very important one. When working with LibreOffice Writer I often have two or even three windows open on the same file:
- the first one in it for the place I currently work.
- a secondary place, from which I might cut or extract information, which I find out that it should be moved to the current position 1, where it fits better,
- a third one just to do searches across the notebook without disturbing the work position any of the other windows.
I asked the developers about this a long time ago, they made a note of the suggestion, but nothing has happened until today. You are not the first to ask about it.
Multiple windows, in each of which you can edit the document at the point opened in it, are extremely important! All the proposals with a shadow copy that you can only read or from which you can only copy are impractical and you are constantly thrown off track with them if you want to fix even small errors or imperfections.
Of course, this is not easy, because the several views can overlap. Or a larger introduction may happen at a place in one of the other windows, which lies before the current one. Inserted pictures are less a problem, LibreOffice shows how this finally has to work even if text flows around inserted pictures. Dynamic content might pose some questions.
The position of the window contents must not change, as long as the change in one window does not protrude into another one. There are quite a few special cases to consider (e.g. if collapsing of cell brackets works on all open windows onto the same file simultaneously: To make things easily manageable, this should be the case in the first try. However once we get that, it wiill not take long until someone will ask to be able to collapse cell bracket structures in one view but leave them untouched in all others!.
But LibreOffice, Microsoft Word etc. can do this with the function "New Window" since more than 10 years! (They don't have the cell collapsing feature, however). The developers at WRI could also copy how the others did multiple views on one document. Hopefully the developers of WRI are not too noble to brilliantly imitate practical solutions of others into their own context!
Multiple windows where you can edit the document each time where it is open is extremely important! All those suggestions with a shadow copy that you can only read or copy from are impractical, and they constantly throw you off track when you want to fix even minor errors or imperfections.
Of course, this is not easy, because the different views may accidentally overlap once, or a major introduction at a location in one of the other windows that is in front of the current one in the window may not change the position of the window contents there, as long as the change in the other window does not intrude into the one currently being viewed. There are quite a few special cases to consider. But LibreOffice, Microsoft Word etc. have been able to do this with the "New Window" function for more than 10 years! WRI's developers could also look at how the others do multiple views in a document. Hopefully the developers of WRI are not too fine to imitate practical solutions of others brilliantly in their own context!
In recent years, Mathematica has featured many admirable advances in mathematics. However, it has quite a few quirks that it had over 25 years ago in dhte user interface and in its editor. e.g. the idiosyncratic automatic indentation, the inability to use tabs, missing shortcuts for effective navigation in notebooks by keyboard actions and so on!
