After writing the above, I realized that line scroll only touches editor.py, not codecontext.py.  On the other hand, the next item, 8. jump to context line did have to wait.  Replacing Label with Text will require explicit height setting with each context change.  The click handler will be a simplified version of the scroll handler you just wrote.  Jumping to a line will look much better when it jumps to a whole rather than a fractional line.  Again, one of us should say something before starting.