refname_is_safe(): improve docstring

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jeff King <peff@peff.net>

refs.c

@@ -341,13 +341,17 @@ static struct ref_dir *get_ref_dir(struct ref_entry *entry)
 }
 
 /*
- * Check if a refname is safe.
- * For refs that start with "refs/" we consider it safe as long they do
- * not try to resolve to outside of refs/.
+ * Return true iff refname is minimally safe. "Safe" here means that
+ * deleting a loose reference by this name will not do any damage, for
+ * example by causing a file that is not a reference to be deleted.
+ * This function does not check that the reference name is legal; for
+ * that, use check_refname_format().
  *
- * For all other refs we only consider them safe iff they only contain
- * upper case characters and '_' (like "HEAD" AND "MERGE_HEAD", and not like
- * "config").
+ * We consider a refname that starts with "refs/" to be safe as long
+ * as any ".." components that it might contain do not escape "refs/".
+ * Names that do not start with "refs/" are considered safe iff they
+ * consist entirely of upper case characters and '_' (like "HEAD" and
+ * "MERGE_HEAD" but not "config" or "FOO/BAR").
  */
 static int refname_is_safe(const char *refname)
 {