The problem: When you use redundancy, i.e., create multiple notes about the same topic, you often want to have the same content in the extra field, or at least parts of the same content.
As of now, the best method for this is, as far as I know, a combination of two add-ons:
- This will copy the exact content (with formatting etc.) from one note to one or more other notes.
- But this method still requires copying and pasting content every time. It is still cumbersome.
There’s also copy note contents to new Add window. But this works only when you want to create a totally new note, not when you want to edit two or more existent notes.
There is Frozen fields, but it is even more limited: It only works when you are creating multiple notes in a row.
My suggestion: I think it would much less cumbersome with a kind of reference. This means to enter a string in a field (esp. the Extra field). The function of the string is that it is a reference to a certain field of a certain note. Not the string will be displayed on the card, but the content of the referenced field.
Inspiration: Maybe you are familiar with KeePass. In KeePass you can duplicate entries. Here, you can create a reference from one password field to the password field of another entry. When you copy the password from the entry with the reference, you don’t copy the referencing text, but the referenced password.
PS: I have made the same suggestion in r/Anki.