-The real name of the file visited in the current buffer,
-or nil if not visiting a file. This is the result of passing
-buffer-file-name to the `file-truename' function. Every buffer has
-its own value of this variable. This variable is automatically
-maintained by the functions that change the file name associated
-with a buffer.
+The real name of the file visited in the current buffer, or nil if not
+visiting a file. This is the result of passing `buffer-file-name' to the
+`file-truename' function. Every buffer has its own value of this variable.
+Code that changes the file name associated with a buffer maintains the
+invariant `(equal buffer-file-truename (file-truename buffer-file-name))'.