Expression is a symbol that represents an ordinary Mathematica expression in Read and related functions.
LegendAppearance is an option for charting functions that specifies the appearance of any legends that are generated.
LinkProtocol is an option to LinkLaunch, Install, and related functions that specifies the underlying data transport protocol to use for a new MathLink link.
LogicalExpand[expr] expands out logical combinations of equations, inequalities, and other functions.
MatchLocalNames is an option for Trace and related functions that specifies whether symbols such as x should match symbols with local names of the form x$nnn.
Modal
(Built-in Mathematica Symbol) Modal is an option to functions such as CreateDialog that specifies whether the dialog that is created should be modal to the Mathematica front end.
Modulus
(Built-in Mathematica Symbol) Modulus -> n is an option that can be given in certain algebraic functions to specify that integers should be treated modulo n.
MousePosition[] gives the current mouse position in the notebook front end. MousePosition["coords"] gives the mouse position with respect to the specified coordinate ...
NotebookObject[fe, id] is an object that represents an open notebook in the front end.
NullWords is an option for Read and related functions which specifies whether null words should be taken to exist between repeated word separators.