Copied from SuperiorShaymin's minecraftforum.net post

Technical info:
MCPE device: iPhone 6 on ios 9 non Jailbroken
MCPE: vanilla 0.12.3 on max settings

So I've been playing on this one world for a while now, so much so that the file size is 110.1 MB. Seeing the file size, I assumed that I've reached the maximum world size, but I haven't been able to find any information to confirm this. The odd thing is that I'm able open the world on the Windows 10 version. If you can confirm my suspicions, or tell me what's actually going on, that would be great.