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The following words are reserved keywords in LSL:

• state: To declare states and change to another state.
• default: The default state.
• if: Check if a condition is true and take different actions depending on the outcome.
• else: Optional part of an if statement that executes when the condition is false.
• while: Loop while a condition is true, or don't execute the loop statements at all if the condition is false.
• do: Loop while a condition is true; the loop executes at least once.
• for: Loop while a condition is true, executing an expression at start and another one while looping.
• return: Return from an event or user function, possibly returning a value.
• jump: Jump to another location within the current function.
• TRUE: Constant for the value 1, treated especially by the compiler.
• FALSE: Constant for the value 0, treated especially by the compiler.
• event: Reserved keyword that does nothing. Do not use.
• print: Obsolete debug message printing method that does nothing. Do not use; use llOwnerSay or similar instead.

In addition to all these, all types, events and constants are also reserved words, meaning you can't use them as names for your own variables, parameters or functions. The library functions are not reserved words (you can't define a function with a name of a library function, because they are in the global namespace, but you can use the same name for your own variables or parameters — not that you would want to, though).

See also a list of the symbols allowed.