Added extra comments to ref_internal.h

Author: ThomasHickman

ref_internal.h

@@ -40,8 +40,11 @@ extern "C" {
  */
 typedef struct {
     hFILE_wrapper base;
+    // length: length of the inner file
     int length;
-    char* file_name; // NOTE: this is set to NULL if this is an in-memory hFILE
+    // file_name: NOTE: this is set to NULL if this is an in-memory hFILE
+    char* file_name;
+    // mf: This is stored if there is an open mFILE, with mmapped memory. This is closed on hclose
     mFILE* mf;
     int is_mem_hfile;
 } hFILE_ref;