TraceAbove is an option for Trace and related functions which specifies whether to include evaluation chains which contain the evaluation chain containing the pattern form ...

TraceBackward is an option for Trace and related functions which specifies whether to include preceding expressions on the evaluation chain that contains the pattern form ...

TraceForward is an option for Trace and related functions which specifies whether to include later expressions on the evaluation chain that contains the pattern form sought.

$RecursionLimit gives the current limit on the number of levels of recursion that Mathematica can use.

"EvaluatorHalt" is a front end token that interrupts the current evaluation and displays the evaluation stack.

ReturnPacket[expr] is a MathLink packet that contains the expression expr, the result of an EvaluatePacket evaluation.

"EvaluateCells" is a front end token that sends the selected cells to the kernel for evaluation.

"EvaluatorAbort" is a front end token that aborts the kernel operation in the specified kernel.

StackComplete[expr] evaluates expr with intermediate expressions in evaluation chains included on the stack.

"EvaluateInitialization" is a front end token that evaluates all the initialization cells in a notebook.