Add zero-indexed register

src/input_handler.cc

@@ -198,6 +198,7 @@ constexpr StringView register_doc =
     "%:     buffer name\n"
     ".:     selection contents\n"
     "#:     selection index\n"
+    "$:     selection index (zero-indexed)\n"
     "_:     null register\n"
     "\":     default yank/paste register\n"
     "@:     default macro register\n"

src/main.cc

@@ -436,6 +436,17 @@ void register_registers()
             return res;
         }));
 
+    register_manager.add_register('$', make_dyn_reg(
+        "$",
+        [](const Context& context) {
+            const size_t count = context.selections().size();
+            StringList res;
+            res.reserve(count);
+            for (size_t i = 0; i < count; ++i)
+                res.push_back(to_string((int)i));
+            return res;
+        }));
+
     for (size_t i = 0; i < 10; ++i)
     {
         register_manager.add_register('0'+i, make_dyn_reg(

src/register_manager.cc

@@ -67,6 +67,7 @@ static const HashMap<StringView, Codepoint> reg_names {
     { "percent", '%' },
     { "dot", '.' },
     { "hash", '#' },
+    { "dollar", '$' },
     { "underscore", '_' },
     { "colon", ':' }
 };