diff --git a/source/mijin/util/string.hpp b/source/mijin/util/string.hpp
index f3a1532..76a3a60 100644
--- a/source/mijin/util/string.hpp
+++ b/source/mijin/util/string.hpp
@@ -350,6 +350,22 @@ constexpr bool toNumber(std::basic_string_view<TChar, TTraits> stringView, TNumb
     return toNumber(asString, outNumber, base);
 }
 
+template<typename TChar>
+[[nodiscard]]
+constexpr bool isDecimalChar(TChar chr) noexcept
+{
+    return (chr >= TChar('0') && chr <= TChar('9'));
+}
+
+template<typename TChar>
+[[nodiscard]]
+constexpr bool isHexadecimalChar(TChar chr) noexcept
+{
+    return isDecimalChar(chr)
+        || (chr >= TChar('A') && chr <= TChar('F'))
+        || (chr >= TChar('a') && chr <= TChar('f'));
+}
+
 namespace pipe
 {
 struct Join