IntervalUnion[interval_1, interval_2, ...] gives the interval representing the set of all points in any of the interval_i.
OpenAppend["file"] opens a file to append output to it, and returns an OutputStream object.
OptionValue[name] gives the value of name in options matched by OptionsPattern. OptionValue[f, name] gives the value of name for options associated with the head f. ...
OutputSizeLimit is an option for notebooks which specifies the maximum size in bytes of expressions that will automatically be output in their entirety.
PageFooterLines is an option for notebooks that specifies whether a horizontal line is inserted at the bottom of each page when the notebook is printed.
PageHeaderLines is an option for notebooks that specifies whether a horizontal line is inserted at the top of each page when the notebook is printed.
Replace
(Built-in Mathematica Symbol) Replace[expr, rules] applies a rule or list of rules in an attempt to transform the entire expression expr. Replace[expr, rules, levelspec] applies rules to parts of expr ...
SendMail[rules] sends an email message built up from the elements specified in rules.
Splice
(Built-in Mathematica Symbol) Splice["file"] splices Mathematica output into an external file. It takes text enclosed between < * and * > in the file, evaluates the text as Mathematica input, and replaces ...
StreamPoints is an option to StreamPlot, ListStreamPlot, and related functions that determines how many streamlines to draw.