Assign a value or values to a variable.

@set(identifier, expression)

@set(identifier, expression1, expression2, ...)

Assign a value or values to a variable only if the variable is empty.

@set(identifier, expression)

@set(identifier, expression1, expression2, ...)

Clear a variable.

@unset(identifier)

Push a value onto the back of an array.

@push(identifier, expression)

Pop a value off the back of an array.

@pop(target identifier, array identifier)