[COMMITTED] pkl-rt-2.pk: Add comment explaining the reason for the file

[Mohammad-Reza Nabipoor]

* libpoke/pkl-rt-2.pk: Add comment.
---
 libpoke/pkl-rt-2.pk | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/libpoke/pkl-rt-2.pk b/libpoke/pkl-rt-2.pk
index 09063446..745af2b6 100644
--- a/libpoke/pkl-rt-2.pk
+++ b/libpoke/pkl-rt-2.pk
@@ -16,6 +16,13 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+/* Any function that uses `format' cannot be used in `pkl-rt-1'.
+   The reason why the problem is happening is that `format' is using
+   `pkl_asm_call' to call `_pkl_reduce_string_array' and `pkl_asm_call'
+   relies on the global environment in the compiler and at that time the
+   on-going environment is not added yet.
+   So we have to put functions that use `format' here, in `pkl-rt-2'.  */
+
 /* Assertion function.
 
    The compiler transforms assert statement to invocation of this
-- 
2.34.1