auctex: Automatic Local

 
 5.5.3 Automatic Customization for a Directory
 ---------------------------------------------
 
 AUCTeX can update the style information about a file each time you save
 it, and it will do this if the directory 'TeX-auto-local' exists.
 'TeX-auto-local' is by default set to '"auto"', so simply creating an
 'auto' directory will enable automatic saving of style information.
 
    The advantage of doing this is that macros, labels, etc.  defined in
 any file in a multifile document will be known in all the files in the
 document.  The disadvantage is that saving will be slower.  To disable,
 set 'TeX-auto-local' to nil.
 
  -- User Option: TeX-style-local
      Directory containing hand generated TeX information.
 
      These correspond to TeX macros found in the current directory.
 
  -- User Option: TeX-auto-local
      Directory containing automatically generated TeX information.
 
      These correspond to TeX macros found in the current directory.