Bu konu Flash’ın help’inde de aynen şöyle anlatılıyor:

asfunction Availability Flash Player 5.

Usage asfunction:function:Function,"parameter":String

Parameters function An identifier for a function.

parameter A string that is passed to the function named in the function parameter.

Returns Nothing. Description Protocol; a special protocol for URLs in HTML text fields. In HTML text fields, text can be linked using the HTML A tag. The HREF attribute of the A tag contains a URL that can be for a standard protocol such as HTTP, HTTPS, or FTP. The asfunction protocol is an additional protocol that is specific to Flash, which causes the link to invoke an ActionScript function.

Example In the following example, the playMP3() function is defined. The TextField object list_txt is created and set so HTML text can be rendered. The text Track 1 and Track 2 are links inside the text field. The playMP3() function is called when the user clicks either link and plays the MP3 that is passed as a parameter of the asfunction call.

var myMP3:Sound = new Sound();
function playMP3(mp3:String) {
  myMP3.loadSound(mp3, true);
  myMP3.onLoad = function(success) {
    if (!success) {
      // code to handle errors here
    }
  };
}
this.createTextField("list_txt", this.getNextHighestDepth(), 0, 0, 200, 100);
list_txt.autoSize = true;
list_txt.html = true;
list_txt.multiline = true;
list_txt.htmlText = "<a href=\"asfunction:playMP3,track1.mp3\">Track 1</a><br>";
list_txt.htmlText += "<a href=\"asfunction:playMP3,track2.mp3\">Track 2</a><br>";

When you click a link, the MP3 sound file streams in Flash Player.