/ForestLevel:{0| |3|4} The default forest functional level when creating a new forest is Windows Server 2003 (2); do not ...

/ForestLevel:{0|<2>|3|4}
The default forest functional level when creating a new forest is Windows Server 2003 (2); do not use this switch when promoting a domain controller in an existing forest
Specifies the forest functional level when creating a new forest. A value of 0 specifies Windows 2000. A value of 2 specifies Windows Server 2003. A value of 3 specifies Windows Server 2008. A value of 4 specifies Windows Server 2008 R2.