La verdad es que de ingles, se poco:
[quote= Flash Help]A SWF file of any version may use this property, but is only supported in Flash Player 8 or later. Thus you can examine this property, for example, from a version 7 SWF file playing in Flash Player 8. This all-versions support means that, if you publish for a version earlier than 8, you will not know at publish time whether this property will be supported at playback time. Thus, in a SWF file of version 7 or earlier, this property has an undefined value; that should happen only when the player version (indicated by flash.system.Capabilities.version) is earlier than 8. In that situation, you can determine the sandbox type according to whether the SWF file is a local file or not. If it is a local file, Flash Player will classify the SWF file as localTrusted. (Before Flash Player 8, this was how all local content was treated.) If it is not a local file, Flash Player will classify the SWF file as remote.[/quote]
No se si sea lo que necesitas pero por que no entiendo bien de que hablan.