By default, slice guides are placed at 25% (or one-fourth) of the symbol’s width and height from the edge of the symbol. In symbol-editing mode, the slice guides appear as dotted lines superimposed on the symbol. The slice guides don’t snap when you drag them on the pasteboard. The guides do not appear when the symbol is on the Stage.
For video tutorials about 9-slice scaling, see:
Enable 9-slice scaling for an existing
movie clip symbol
Edit a 9-slice-enabled movie clip
symbolSelect an instance of the symbol on the Stage and right-click (Windows) or Control-click (Macintosh), and select Edit.
Select the symbol in the Library and right-click (Windows) or Control-click (Macintosh), and select Edit.
Double-click the symbol in the Library.