The Option Inspector

Many aspects of the Wolfram System front end such as the styles of cells, the appearance of notebooks, or the parameters used in typesetting are controlled by options. For example, text attributes such as size, font, and color each correspond to a separate option. You can set options by directly editing the expression for a cell or notebook. But in most cases it is simpler to use the Option Inspector.
The Option Inspector is a special tool for viewing and modifying option settings. It provides a comprehensive listing of all front end options, grouped according to their function. You can specify not only the setting for an option, but also the level at which it will take effect: globally, for an entire notebook, or for a selection.
To use the Option Inspector, choose Format Option Inspector. This brings up a dialog box with two popup menus on top. The popup menu on the left specifies the level at which options will take effect. The popup menu on the right allows you to choose if you want the options listed by category, alphabetically, or as text.
Inheritance of Options
The Option Inspector allows you to set the value of an option on three different levels. In increasing order of precedence, the levels are as follows.
Global Preferencessettings for the entire application
Selected Notebooksettings for an entire notebook
Selectionsettings for the current selection, e.g. for a group of cells, a single cell, or text within a cell
The levels lower in the hierarchy inherit their options from the level immediately above them. For example, if a notebook has the option Editable set to True, by default all cells in the notebook will be editable.
You can, however, override the inherited value of an option by explicitly changing its value. For example, if you do not want a particular cell in your notebook to be editable, you can select the cell and set Editable to False. This inheritance property of options provides you with a great deal of control over the behavior of the front end, since you can set any option to have different values at each level, as required.
Note: At each level, only the options that can be set at that level are listed in the Option Inspector. All other options appear dimmed, indicating that they cannot be changed unless you go to a higher or lower level.
Searching for an Option
To search for a specific option, begin typing its name in the text field. The Option Inspector goes to the first matching option. Press Enter to go to the next matching item on the list. (On Macintosh, the Option Inspector displays all matching options at once.)
Each line in the list of options gives the option name followed by its current value. You can change the option's value by choosing from the popup menu next to the option setting, or by selecting the option and clicking the value, typing over it, and pressing Enter.
When you start the Wolfram System for the first time, the values of all the options are set to their default values. Each time you modify one of the options, a symbol appears next to it, indicating that the value has been changed. Clicking the symbol resets the option to its default value.
Setting Options: An Example
Suppose you want to draw a frame around a cell. The option that controls this property of a cell is called CellFrame.
To Draw a Frame around a Cell:

1.  Select the cell by clicking the cell bracket.

2.  Choose Format Option Inspector to open the Option Inspector window.

3.  Choose Selection from the first popup menu.

4.  Click Cell Options Display Options. This gives a list of all options that control how a cell is displayed in the notebook.

5.  Type True into the value field next to the option CellFrame. An icon appears next to the option, indicating that its value has been changed. The cell that you selected now has a frame drawn around it.

Alternatively, you can begin typing cellframe in the text field. This leads you directly to the CellFrame option without having to search by category. This feature provides a useful way to locate an option if you are unsure of the category it belongs in.