HelpBrowserSettings -> {opt_1 -> val_1, opt_2 -> val_2, ...} is a global option that specifies settings for the legacy Help Browser.
InputAssumptions is an option for WolframAlpha that specifies assumptions for current query input.
LinebreakAdjustments is an option for selections that sets parameters used for calculating where automatic line breaks should be inserted.
PhaseMargins[sys] gives the phase margins of a linear time-invariant system sys.
PrivateEvaluationOptions -> {opt_1 -> val_1, opt_2 -> val_2} is an option for selections that specifies settings for evaluation-related suboptions.
expr //. rules repeatedly performs replacements until expr no longer changes.
SpellingOptions -> {opt_1 -> val_1, opt_2 -> val_2, ...} is an option for notebooks that specifies settings for spell checking.
SyntaxForm is an option for InterpretationBox and TagBox objects that specifies the precedence level to use when the InterpretationBox or TagBox is considered as an operator.
ValueQ
(Built-in Mathematica Symbol) ValueQ[expr] gives True if a value has been defined for expr, and gives False otherwise.
$Pre
(Built-in Mathematica Symbol) $Pre is a global variable whose value, if set, is applied to every input expression.