diff --git a/include/tcframe/validator/core.hpp b/include/tcframe/validator/core.hpp
index 3770ccc..6189960 100644
--- a/include/tcframe/validator/core.hpp
+++ b/include/tcframe/validator/core.hpp
@@ -1,9 +1,13 @@
+#pragma once
 
+#include <string>
 #include <type_traits>
+#include <vector>
 
 using std::enable_if_t;
 using std::is_arithmetic_v;
 using std::size_t;
+using std::string;
 using std::vector;
 
 namespace tcframe {
@@ -52,11 +56,6 @@ VectorElementValidator<T> eachElementOf(const vector<T>& val) {
     return VectorElementValidator(val);
 }
 
-template<typename T, typename = ScalarType<T>>
-VectorElementValidator<T> eachElementOf(vector<T>&& val) {
-    return VectorElementValidator(val);
-}
-
 template<typename T, typename = ScalarType<T>>
 struct VectorElementsValidator {
 private:
@@ -114,4 +113,25 @@ VectorElementsValidator<T> elementsOf(const vector<T>& val) {
     return VectorElementsValidator(val);
 }
 
+struct StringElementValidator {
+private:
+    const string& val;
+
+public:
+    explicit StringElementValidator(const string& _val) : val(_val) {}
+
+    bool isBetween(char minVal, char maxVal) {
+        for (char v : val) {
+            if (!valueOf(v).isBetween(minVal, maxVal)) {
+                return false;
+            }
+        }
+        return true;
+    }
+};
+
+StringElementValidator eachCharacterOf(const string& val) {
+    return StringElementValidator(val);
+}
+
 }
diff --git a/test/unit/tcframe/validator/CoreValidatorTests.cpp b/test/unit/tcframe/validator/CoreValidatorTests.cpp
index 03034fa..c3cf87f 100644
--- a/test/unit/tcframe/validator/CoreValidatorTests.cpp
+++ b/test/unit/tcframe/validator/CoreValidatorTests.cpp
@@ -66,4 +66,11 @@ TEST_F(CoreValidatorTests, elementsOf_areUnique) {
     EXPECT_TRUE(elementsOf(vector<char>{'a', 'x', 'd', 'g', 'h'}).areUnique());
 }
 
+TEST_F(CoreValidatorTests, eachCharacterOf_isBetween) {
+    EXPECT_FALSE(eachCharacterOf("BCDEF").isBetween('B', 'E'));
+    EXPECT_FALSE(eachCharacterOf("BCDEF").isBetween('C', 'F'));
+    EXPECT_TRUE(eachCharacterOf("BCDEF").isBetween('B', 'F'));
+    EXPECT_TRUE(eachCharacterOf("BCDEF").isBetween('A', 'G'));
+}
+
 }