ShowAutoStyles is an option for Cell that specifies whether styles that are specified to be automatically used for various syntactic and other constructs should be shown.
ShowCellLabel is an option for Cell that specifies whether to display the label for a cell.
Skeleton[n] represents a sequence of n omitted elements in an expression printed with Short or Shallow. The standard print form for Skeleton is <<n>>.
Skip
(Built-in Mathematica Symbol) Skip[stream, type] skips one object of the specified type in an input stream. Skip[stream, type, n] skips n objects of the specified type.
Spacings is an option to Grid and related constructs that specifies the spacings to leave between successive objects.
Superscript[x, y] is an object that formats as x^y.
TableDirections is an option for TableForm and MatrixForm which specifies whether successive dimensions should be arranged as rows or columns.
XMLElement[tag, {attr_1 -> val_1, ...}, {data_1, ...}] represents an element in symbolic XML.
$MaxRootDegree specifies the maximum degree of polynomial to allow in Root objects.
$NumberMarks gives the default value for the option NumberMarks, which specifies whether ` marks should be included in the input form representations of approximate numbers.