Allow ubiquitous tokens to also be used in grammar rules

src/runtime/tree.h

@@ -0,0 +1,26 @@
+#ifndef RUNTIME_TREE_H_
+#define RUNTIME_TREE_H_
+
+#include "tree_sitter/runtime.h"
+
+struct ts_tree {
+    ts_symbol symbol;
+    size_t ref_count;
+    size_t offset;
+    size_t size;
+    int is_extra;
+    union {
+        struct {
+            size_t count;
+            size_t immediate_count;
+            struct ts_tree **contents;
+        } children;
+        struct {
+            char lookahead_char;
+            size_t expected_input_count;
+            const ts_symbol *expected_inputs;
+        } error;
+    } data;
+};
+
+#endif  // RUNTIME_TREE_H_