# Why only up to two \[Prime] superscripts are interpreted as derivatives?

I noticed that only up to two \[Prime] superscripts are interpreted as derivatives. Is there a reason for this restriction? Is it documented?

\!$$\*SuperscriptBox["Sin","\[Prime]"][x]$$
(* Cos[x] *)

\!$$\*SuperscriptBox["Sin","\[Prime]\[Prime]"][x]$$
(* -Sin[x] *)

\!$$\*SuperscriptBox["Sin","\[Prime]\[Prime]\[Prime]"][x]$$
(* (Sin^\[Prime]\[Prime]\[Prime])[x] *)

The regular apostrophe can be used any number of times though:

Sin'''[x]
(* -Cos[x] *)
-
It is sort-of Documented in that only Prime and DoublePrime are defined.. –  george2079 Oct 21 '13 at 18:00