Add $$ and $_.
diff --git a/lib/ascii.dart b/lib/ascii.dart
index 94f7419..663bcba 100644
--- a/lib/ascii.dart
+++ b/lib/ascii.dart
@@ -113,6 +113,8 @@
/// Character '#'.
const int $hash = 0x23;
/// Character '$'.
+const int $$ = 0x24;
+/// Character '$'.
const int $dollar = 0x24;
/// Character '%'.
const int $percent = 0x25;
@@ -272,6 +274,8 @@
/// Character '^'.
const int $hat = 0x5E;
/// Character '_'.
+const int $_ = 0x5F;
+/// Character '_'.
const int $underscore = 0x5F;
/// Character '_'.
const int $underline = 0x5F;