Allowed

  • Basic syntax
  • Types:
    • Booleans
    • Integers
    • Floating point numbers
    • Strings
    • Arrays
    • NULL
  • Variables:
    • Pre-named
  • Expressions
  • Operators:
    • Arithmetic
    • Assignment
    • Bitwise
    • Comparison
    • Incrementing/Decrementing
    • Logical
    • String
    • Array
  • Control Structures
  • Functions:
    • Internal (built-in):
      • Mathematical
      • Variable-handling
      • Strings
      • Array
  • References

Disallowed

  • Basic syntax:
    • Comments
    • HTML
  • Types:
    • Objects
    • Resource
  • Variables:
    • Predefined variables
    • Variable variables
    • Variables from outside PHP
  • Constants
  • Operators:
    • Execution
    • Type
  • Control structures:
    • Require
    • Include
  • Functions:
    • User-defined functions
    • Variable-functions
  • Classes and Objects
  • Namespaces
  • Exceptions
  • (everything else)