Maximum length of kill ring before oldest elements are thrown away. These operations are essential for customizing the variable. For example, you can type M-d , then insert another number. Editing the value does not actually set the option variable. To do that, you must set the option.
Some options have a small fixed set of possible legitimate values.
These options don't let you edit the value textually. Some options have values with complex structure. For example, the value of load-path is a list of directories. Each directory in the list appears on a separate line, and each line has several editable or active fields. You can edit any of the directory names.