The double-linked list was just an example. Could also have been any other list container for Unicode code points, where each code point uses a fixed size of me

The double-linked list was just an example. Could also have been any other list container for Unicode code points, where each code point uses a fixed size of memory (at least 21 bits). You might even use a data structures where a 'base' character with (optional) combining characters are treated as a single unit, because for many operations they should be treated as a unit.