Where is that documented.
At official documentation for the TStringGrid, your specific method you find
here.
I hope this helps.
Steps to reproduce using official help ->
1. Open the official
TStringGrid documentiation.
2. Search for your method (Clean), you will find out that it is not listed here so go one step above from where TStringGrid comes from
3. You will land at
TCustomStringGrid and there you find "Clean" listed.
I hope it helps and sorry that I also answered.