ff-special-constructs

ff-special-constructs is a variable defined in `find-file.el'.
Its value is

(("^#\\s *\\(include\\|import\\)\\s +[<\"]\\(.*\\)[>\"]" lambda nil
  (buffer-substring
   (match-beginning 2)
   (match-end 2))))

Documentation:
List of special constructs recognized by `ff-treat-as-special'.
Each element, tried in order, has the form (REGEXP . EXTRACT).
If REGEXP matches the current line (from the beginning of the line),
`ff-treat-as-special' calls function EXTRACT with no args.
If EXTRACT returns nil, keep trying. Otherwise, return the
filename that EXTRACT returned.

You can customize this variable.