I have done some googling and it appears this can be acheived by passing -swf-version=13 into the compiler. It tried doing this point at my applciation level project and a subsystem SWC level project and I still show a compiler error. Would really be nice if there was a nice 4.5 example of using this feature with a fallback mechanism for 10.3 users.
You should also need a newer playerglobal.swc.
What do you mean by fallback? As long as you have the swf compiled for FP 11 the classes will be there . If you want to load some external swf which might not have it I think you could for FlexVersion.compatibilityVersion < FlexVersion.VERSION_X_X and have some custom logic ...
By Fallback, I mean I want to be able to use the Native JSON support for people that have Flash player 11 installed and fall back to the a3corelib for people without Flash player 11 installed.
I would like to do the same thing but when I compile my app, compilation fails.
Even livedocs example (http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/JSON.html#includeExampl esSummary) does not compile. I tried with Flex 4.5 (swf-version: 11) and Flex 4.5.1 (swf-version: 13).
flex/bin/mxmlc -swf-version=13 -target-player=11 test.as -debug=true -incremental -optimize -o test.swf -sp .
Compiler Adobe Flex (mxmlc)
Version 4.5.0 build 19786
/opt/flex/frameworks/flex-config.xml(56): Error: unable to open 'libs/player/11.2/playerglobal.swc'
make: *** [test.swf] Error 1
I finally found the solution :
1) Download the last Flex stable version (Open Source Flex SDK) : http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4.5
2) Download the last playerglobal.swc : http://fpdownload.macromedia.com/pub/flashplayer/updaters/11/playerglobal11_0.swc
3) Rename playerglobal11_0.swc to playerglobal.swc and move it into /opt/flex/frameworks/libs/player/11.2/
That's all !