LICE implements the following extentions that are likewise present
in existing compilers like GCC/Clang.

- Dollar signs in Identifier Names:
    http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html

- Referring to a Type with typeof:
    http://gcc.gnu.org/onlinedocs/gcc/Typeof.html

- Conditionals with Omitted Operands:
    http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html

- Statements and Declarations in Expressions
    http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html

- Structures with No Members
    http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html

- Non-Constant Initializers
    http://gcc.gnu.org/onlinedocs/gcc/Initializers.html

- Case Ranges
    http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html

- Cast to a Union Type
    http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html

- The Character <ESC> in Constants
    http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html

- Incomplete enum Types
    http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html

- Binary constants using the '0b' prefix
    http://gcc.gnu.org/onlinedocs/gcc/Binary-constants.html

- Arithmetic on void- and Function-Pointers
    http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html

- Labels as Values
    http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html

- Arrays of Length Zero
    http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

- Getting the Return or Frame Address of a Function
    http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html
    __builtin_return_address only currently.