RemoveAlphaChannel[image] removes all opacity information from image.RemoveAlphaChannel[image, c] removes opacity by blending all pixels with the background color c.
RenameFile["file_1", "file_2"] renames file_1 to file_2.
RightArrow[x, y, ...] displays as x \[RightArrow] y \[RightArrow] ....
ScriptMinSize is an option for Style that specifies the minimum font size to use in rendering subscripts, etc.
ScrollPosition is an option for Pane that specifies the scroll position of the contents of the pane.
ShowCellBracket is an option for Cell that specifies whether to display the bracket that indicates the extent of the cell.
ShowSelection is an option to Notebook, Cell, and Style that specifies whether to show the current selection highlighted.
SignPadding is an option for NumberForm and related functions that specifies whether padding should be inserted after signs.
StreamPosition[stream] returns an integer that specifies the position of the current point in an open stream.
Streams
(Built-in Mathematica Symbol) Streams[] gives a list of all streams that are currently open. Streams["name"] lists only streams with the specified name.