In Flash there is option ( fullScreenSourceRect ) to play a specific region in full-screen mode. This is not implemented in HTML target. How easy will be to add that option or is there any other way to do it ? Here is information from Adobe : http://help.adobe.com/en_US/AS2LCR/Flash_10.0/help.html?content=00001538.html
I believe it would happen here:
https://github.com/openfl/openfl/blob/develop/openfl/display/Stage.hx#L1764-L1786
In theory, the __displayMatrix could be set to scale and position based upon a fullScreenSourceRect property
It would have to be conditional on fullscreen, though