Declaration: TStringList.Assign(Source: TStringList);
The method Assign copies the contents of another string list (parameter Source) overwriting the current string list.

Hint: In general, the statement Destination := Source; is not the same as the statement Destination.Assign(Source);. The first statement makes Destination referring to the same object as Source, whereas the second statement copies the contents of the object referenced by Source into the object referenced by Destination.