LineIndent is an option for Cell, StyleBox and StyleForm which specifies how many ems of indentation to add at the beginnings of lines for each level of nesting in an expression.
The typical default setting is LineIndent->1.
The setting for LineIndent determines the amount of indentation that will be inserted after any explicit Return is entered when AutoIndent->True.
See also: LineIndentMaxFraction, PageWidth.
New in Version 3.