Added Flexibility: Using SmartClips
There is a fundamental problem with the ScriptClip in its current form. Examine the code again:

_parent._alpha+=5;

Recall that we want to make scripts as generic as possible, so we have the flexibility to use them throughout the movie. Our script has made the target Instance that the script affects generic, but the value of the increment in this case is fixed, currently at 5. What if we want another Instance to fade in to view gradually, with a value of say 3? We’d would have to make another ScriptClip with a different value. This could add up to a number of ScriptClips based on the value of the increment, which is no more efficient than simply including the script in various key frames throughout the movie.
What if we could make the value generic as well? For example, I’m going to change the script from:

_parent._alpha+=5;

to

_parent._alpha+=userValue;

I’ve changed the fixed value (5) into a variable, userValue. By making the ScriptClip into a SmartClip, we can specify the value of the variable userValue each time we use an Instance of the script.alphaFadeIn Symbol. SmartClips allow us to control variables within ActionScript inside of Symbols.