diff --git a/docs/tutorial.md b/docs/tutorial.md
index 2badb6b..0054e34 100644
--- a/docs/tutorial.md
+++ b/docs/tutorial.md
@@ -1484,6 +1484,9 @@ A typical set of String functions includes:
 | lower(), lowercase() | change case to unicode upper                               |
 | upper(), uppercase() | change case to unicode lower                               |
 | trim()               | trim space chars from both ends                            |
+| isEmpty()            | true if string is empty                                    |
+| isNotEmpty()         | true if string is not empty                                |
+| isBlank()            | true if empty or contains only whitespace                  |
 | startsWith(prefix)   | true if starts with a prefix                               |
 | endsWith(prefix)     | true if ends with a prefix                                 |
 | last()               | get last character of a string or throw                    |
diff --git a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjString.kt b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjString.kt
index 92528d8..25ae4d6 100644
--- a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjString.kt
+++ b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjString.kt
@@ -301,6 +301,18 @@ data class ObjString(val value: String) : Obj() {
             ) {
                 thisAs<ObjString>().value.trim().let(::ObjString)
             }
+            addFnDoc("isBlank", "Whether this string is empty or contains only whitespace characters.",
+                returns = type("lyng.Bool"), moduleName = "lyng.stdlib") {
+                ObjBool(thisAs<ObjString>().value.isBlank())
+            }
+            addFnDoc("isEmpty", "Whether this string is empty.",
+                returns = type("lyng.Bool"), moduleName = "lyng.stdlib") {
+                ObjBool(thisAs<ObjString>().value.isEmpty())
+            }
+            addFnDoc("isNotEmpty", "Whether this string is not empty.",
+                returns = type("lyng.Bool"), moduleName = "lyng.stdlib") {
+                ObjBool(thisAs<ObjString>().value.isNotEmpty())
+            }
             addFnDoc(
                 name = "matches",
                 doc = "Whether this string matches the given regular expression or pattern string.",
diff --git a/lynglib/src/commonTest/kotlin/OOTest.kt b/lynglib/src/commonTest/kotlin/OOTest.kt
index 3d3c85b..dbc48a1 100644
--- a/lynglib/src/commonTest/kotlin/OOTest.kt
+++ b/lynglib/src/commonTest/kotlin/OOTest.kt
@@ -779,7 +779,8 @@ class OOTest {
 
     @Test
     fun testOverrideVisibilityRules1() = runTest {
-        eval("""
+        val scope = Script.newScope()
+        scope.eval("""
             interface Base {
                 abstract protected fun foo()
                 
@@ -802,12 +803,70 @@ class OOTest {
             class Derived2: Base {
                 private var value = 42
                 
+                private fun fooPrivateImpl() = value
+                
                 override protected fun foo() {
-                    if( value < 10 ) 10 else value
+                    fooPrivateImpl()
+                    value++
                 }
             }
+            assertEquals("bar!", Derived().bar())
+            val d = Derived2()
+            assertEquals(42, d.bar())
+            assertEquals(43, d.bar())
+        """.trimIndent())
+        scope.createChildScope().eval("""            
             assertEquals("bar!", Derived().bar())
             assertEquals(42, Derived2().bar())
         """.trimIndent())
     }
+    @Test
+    fun testOverrideVisibilityRules2() = runTest {
+        val scope = Script.newScope()
+        scope.eval("""
+            interface Base {
+                abstract fun foo()
+                
+                fun bar() {
+                    // it must see foo() as it is protected and 
+                    // is declared here (even as abstract):
+                    foo()
+                }
+            }
+            class Derived : Base {
+                protected val suffix = "!"
+                
+                private fun fooPrivateImpl() = "bar"
+            
+                override fun foo() { 
+                    // it should access own private and all protected memberes here: 
+                    fooPrivateImpl() + suffix  
+                }
+            }
+            class Derived2: Base {
+                private var value = 42
+                
+                private fun fooPrivateImpl() = value
+                
+                override fun foo() {
+                    fooPrivateImpl()
+                    value++
+                }
+            }
+            assertEquals("bar!", Derived().bar())
+            val d = Derived2()
+            assertEquals(42, d.bar())
+            assertEquals(43, d.bar())
+        """.trimIndent())
+        scope.createChildScope().eval("""            
+            assertEquals("bar!", Derived().bar())
+            assertEquals(42, Derived2().bar())
+            import lyng.serialization
+            for( i in 1..100 ) {
+                val d2 = Lynon.decode(Lynon.encode(Derived2()))
+                assertEquals(42, d2.bar())
+                assertEquals(43, d2.bar())
+            }
+        """.trimIndent())
+    }
 }
\ No newline at end of file