Here is a typical palette of modifiers. Mathematica allows you to use any expression as a subscript. Unless you specifically tell it otherwise, Mathematica will interpret a ...

expr[[i]] or Part[expr, i] gives the i\[Null]^th part of expr. expr[[-i]] counts from the end. expr[[i, j, ...]] or Part[expr, i, j, ...] is equivalent to expr[[i]][[j]] .... ...

All textual and graphical forms in Mathematica are ultimately represented in terms of nested collections of boxes. Typically the elements of these boxes correspond to objects ...

Mathematica allows you to control how the pages in notebooks are laid out for printing. You can give a general specification in a stylesheet, or you can specify details for ...

"TemplateSelection" is a front end token that inserts a function template to the right of the insertion point.

AppendTo[s, elem] appends elem to the value of s, and resets s to the result.

Bottom is a symbol that represents the bottom for purposes of alignment and positioning.

BoxData[boxes] is a low-level representation of the contents of a typesetting cell.

CellChangeTimes is an option to Cell that specifies when changes were made to the cell.

FormatTypeAutoConvert is an option for cells that specifies whether the contents of a cell are automatically converted into a different format when the style of that cell is ...