You want to add a movie clip to your movie from the library without having to create an instance manually at authoring time.
attachMovie( ) method.
You should make a practice of using the
) method to add movie clips to your movies for any
instances that are controlled entirely by ActionScript. The
attachMovie( ) method allows you to add a movie
clip using ActionScript at runtime instead of having to add the movie
clip manually at authoring time. This is advantageous for several
attachMovie( ), you can add movie clips
dynamically. This is extremely important for any movies in which you
need to load movie clips based on user information or data drawn from
an XML file or a database.
It is bad practice to add movie clips to the Stage at authoring time that will be controlled exclusively by ActionScript. Don’t add movie clips to your Stage at authoring time unless they are being manually animated or you need to visually lay them out.
attachMovie( ), you must export the movie
clip Library symbols. Library symbols are automatically exported with
the movie when you create instances of them at authoring time.
However, if a symbol is not explicitly used within the movie as a
manually created instance, it is not automatically included in the
.swf file (this saves space by not including unused symbols). In these cases, you need to tell Flash to export the symbol ...