Local Variables Features

• If a local variable name has a non-nil permanent-local property, then kill-all-local-variables does not kill it. Such local variables are "permanent"---they remain unchanged even if you select a different major mode. Permanent locals are useful when they have to do with where the file came from or how to save it, rather than with how to edit the contents.
• The function make-local-variable now never changes the value of the variable that it makes local. If the variable had no value before, it still has no value after becoming local.
• The new function default-boundp tells you whether a variable has a default value (as opposed to being unbound in its default value). If (default-boundp 'foo) returns nil, then (default-value 'foo) would get an error. default-boundp is to default-value as boundp is to symbol-value.
• The special forms defconst and defvar, when the variable is local in the current buffer, now set the variable's default value rather than its local value.