Show Toolbar toggles toolbar display along the top of a notebook.

WindowElements is a notebook option that specifies the elements to include in the window used to display the notebook on the screen.

Selectable is an option for displayed objects, cells, and notebooks that specifies whether their contents can be selected interactively using the front end.

Bold represents a bold font weight.

CellInformation[obj] gives information about selected cells in the notebook represented by the notebook object obj.

UnderscriptBox[x, y] is the low-level box representation for UnderscriptBox[x, y] in notebook expressions.

Open opens a dialog box for opening an existing file.

FractionBox[x, y] is a low-level formatting construct that represents x/y in notebook expressions.

RadicalBox[x, n] is a low-level box construct that represents the displayed object Power[x, (n)^-1] in notebook expressions.

SqrtBox[x] is a low-level box construct that represents the displayed object Sqrt[x] in notebook expressions.