Inheritance of Options
The Option Inspector allows you to set the value of an option on three different levels. In decreasing order of precedence, the levels are as follows.
Global - to set preferences for the entire application
Notebook - to set preferences for an entire notebook
Selection - to set preferences locally, 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 which 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.