Explain some previously un-stated invariants about the TouchDevelop AST.
Explain some previously un-stated invariants about the TouchDevelop AST.

MetSystem/TouchDevelop,jle33/TouchDevelop,jle33/TouchDevelop,jle33/TouchDevelop,CodeKingdomsTeam/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,CodeKingdomsTeam/TouchDevelop,UIKit0/TouchDevelop,MetSystem/TouchDevelop,sedouard/TouchDevelop,imadityab/FSE-2012-TouchDevelop-old,sedouard/TouchDevelop,Aksoom-Hussain/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,jle33/TouchDevelop,jmptrader/TouchDevelop,UIKit0/TouchDevelop,ntoll/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,MetSystem/TouchDevelop,jmptrader/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,sedouard/TouchDevelop,ntoll/TouchDevelop,CodeKingdomsTeam/TouchDevelop,ntoll/TouchDevelop,jle33/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,imadityab/FSE-2012-TouchDevelop-old,jmptrader/TouchDevelop,imadityab/FSE-2012-TouchDevelop-old,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,jmptrader/TouchDevelop,Aksoom-Hussain/TouchDevelop,CodeKingdomsTeam/TouchDevelop,UIKit0/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,Aksoom-Hussain/TouchDevelop,imadityab/FSE-2012-TouchDevelop-old