I notice that for users, google uses /u/0/ at the end, but going into a document does not have a /u/0/ and just is an ID (e.g., /d/RgerGR534GREGgrrgRGEKUU53/edit?tab=t.0). Each single-page Google Documents document just checks for whether the user is permitted to see the document and then it gives access.
I was wondering why not "?u=0"
I was wondering if it was better to generate programatically each document in a user-tied document list through documents in json through ?u=1, or if it is better to do /u/0/ which contains already the document list. This means that it's not programatically created during the loading, but it is already programatically set up before (the html of the document list, that is). So in other words, based on the reasonings you gave, the Google /u/0/ approach is clearly cleaner, faster, and much more straightforward and reliable in many cases.
By the way, I was wondering whether I should use a ran