tags-file-name is a variable defined in `etags.el'.
Its value is
nil
This variable is safe as a file local variable if its value
satisfies the predicate `stringp'.
Documentation:
File name of tags table.
To switch to a new tags table, setting this variable is sufficient.
If you set this variable, do not also set `tags-table-list'.
Use the `etags' program to make a tags table file.