[MATH] Add HB_OT_MATH_SCRIPT
diff --git a/src/hb-ot-math.h b/src/hb-ot-math.h
index ad8bf14..814e404 100644
--- a/src/hb-ot-math.h
+++ b/src/hb-ot-math.h
@@ -42,6 +42,9 @@
 
 #define HB_OT_TAG_MATH HB_TAG('M','A','T','H')
 
+/* Use with hb_buffer_set_script() for math shaping. */
+#define HB_OT_MATH_SCRIPT HB_TAG('m','a','t','h')
+
 /* Types */
 
 typedef enum {