Octave Symbols
The octave symbols (8va and 15va) act as a “local display transpose” – they shift the display of the score one/two octaves down.
By dragging the end of the dotted line, you can specify exactly which notes are affected by the octave symbol.
Only notes beneath the dotted line are display transposed.
You can also right-click on the octave symbol and select the “Extend (+)” or “Reduce (-)” command to extend it to the next chord or to reduce it.