Related Clues:
- Architect's afterthought
- Like some fees
- Build a new wing, say
- After-market item
- Home improvement
- Building contractor's job
- Saw around soft fold in limb
- Wing, e.g. ... or a hint to answering 17-, 23-, 49- and 56-Across
- Software plug-in
- Optional component
- Bonus feature
- Peripheral device
- Looking back, gesture from father in extension
- Postscript saying Poland's premier writer should be included
- Auto option, e.g