ToContinuousTimeModel[sys] gives the continuous-time approximation of the discrete-time TransferFunctionModel or StateSpaceModel object sys.ToContinuousTimeModel[tf, s] gives ...
TraceOriginal is an option for Trace and related functions which specifies whether to test the form of each expression before its head and arguments are evaluated.
UnsameQ
(Built-in Mathematica Symbol) lhs =!= rhs yields True if the expression lhs is not identical to rhs, and yields False otherwise.
WindowFrame is a notebook option that specifies the type of frame to draw around the window in which the notebook is displayed on the screen.
WordSeparators is an option for Read, Find, and related functions that specifies the list of strings to be taken as delimiters for words.
XMLElement[tag, {attr_1 -> val_1, ...}, {data_1, ...}] represents an element in symbolic XML.
ZeroTest is an option to various linear algebra functions that gives a function to use in testing whether symbolic expressions should be treated as zero.
$FrontEnd is a global variable that specifies to what front end object, if any, the kernel is currently connected.
$MinNumber gives the minimum positive arbitrary-precision number that can be represented on a particular computer system.
$NewSymbol is a global variable which, if set, is applied to the name and context of each new symbol that Mathematica creates.