Mathematica makes it easy to "bulletproof" packages, and prevent features of their environment from affecting their internal operation.
CheckAbort[expr, failexpr] evaluates expr, returning failexpr if an abort occurs.
CreateDirectory["dir"] creates a directory with name dir. CreateDirectory[] creates a directory in the default area for temporary directories on your computer system.
DiracComb[x] represents the Dirac comb function giving a delta function at every integer point. DiracComb[x_1, x_2, ...] represents the multidimensional Dirac comb function.
x /= c divides x by c and returns the new value of x.
HoldPattern[expr] is equivalent to expr for pattern matching, but maintains expr in an unevaluated form.
IntervalMemberQ[interval, x] gives True if the number x lies within the specified interval, and False otherwise. IntervalMemberQ[interval_1, interval_2] gives True if ...
SaveDefinitions is an option to Manipulate and related functions that specifies whether current definitions relevant for the evaluation of the expression being manipulated ...
StackBegin[expr] evaluates expr, starting a fresh evaluation stack.
StackInhibit[expr] evaluates expr without modifying the evaluation stack.