diff --git a/examples/invoke.rs b/examples/invoke.rs
index 417db14..2e7bc38 100644
--- a/examples/invoke.rs
+++ b/examples/invoke.rs
@@ -18,6 +18,7 @@ fn main() {
     // Intrepreter initialization.
     // parity_wasm::ProgramInstance can be parameterized with a custom User error which could be returned from imported functions
     // parity_wasm::DefaultProgramInstance parametrize ProgramInstance with a pre-defined "DummyUserError"
+    // Initializes a default "env" module also.
     let program = parity_wasm::DefaultProgramInstance::with_env_params(
         interpreter::EnvParams {
             total_stack: 128*1024,
@@ -37,7 +38,7 @@ fn main() {
         // Type section stores function types which are referenced by function_section entries
         let type_section = module.type_section().expect("No type section found");
 
-        // A given function name used to find export section entry which contains
+        // Given function name used to find export section entry which contains
         // an `internal` field which points to the index in the function index space
         let found_entry = export_section.entries().iter()
             .find(|entry| func_name == entry.field()).expect(&format!("No export with name {} found", func_name));
@@ -81,7 +82,13 @@ fn main() {
         interpreter::ExecutionParams::from(args)
     };
 
-    // Intialize deserialized module.
+    // Intialize deserialized module. It adds module into It expects 3 parameters:
+    // - a name for the module
+    // - a module declaration
+    // - an optional HashMap of additional external modules (which takes priority over already initialized modules)
+    //   to be:
+    //   - formally validated
+    //   - validated imports against these external modules
     let module = program.add_module("main", module, None).expect("Failed to initialize module");
 
     println!("Result: {:?}", module.execute_export(func_name, execution_params).expect(""));
diff --git a/src/interpreter/module.rs b/src/interpreter/module.rs
index 9f0f044..a81a2ba 100644
--- a/src/interpreter/module.rs
+++ b/src/interpreter/module.rs
@@ -297,7 +297,7 @@ impl<E> ModuleInstance<E> where E: UserError {
 									export_function_type.params(), export_function_type.return_type())));
 							}
 						}
-					}, 
+					},
 					&External::Global(ref global_type) => if global_type.is_mutable() {
 						return Err(Error::Validation(format!("trying to import mutable global {}", import.field())));
 					} else {
@@ -347,15 +347,15 @@ impl<E> ModuleInstance<E> where E: UserError {
 					let mut context = FunctionValidationContext::new(
 						self,
 						externals,
-						&locals, 
-						DEFAULT_VALUE_STACK_LIMIT, 
-						DEFAULT_FRAME_STACK_LIMIT, 
+						&locals,
+						DEFAULT_VALUE_STACK_LIMIT,
+						DEFAULT_FRAME_STACK_LIMIT,
 						function_type.clone());
 
 					let block_type = function_type.return_type().map(BlockType::Value).unwrap_or(BlockType::NoResult);
 					Validator::validate_function(&mut context, block_type, function_body.code().elements())
-						.map_err(|e| { 
-							if let Error::Validation(msg) = e { 
+						.map_err(|e| {
+							if let Error::Validation(msg) = e {
 								Error::Validation(format!("Function #{} validation error: {}", index, msg))
 							} else {
 								e
@@ -474,7 +474,7 @@ impl<E> ModuleInstanceInterface<E> for ModuleInstance<E> where E: UserError {
 					},
 				})
 				.map(|i| *i)
-				.ok_or(Error::Program(format!("unresolved import {}", name))))
+				.ok_or(Error::Program(format!("unresolved export {}", name))))
 	}
 
 	fn table(&self, index: ItemIndex) -> Result<Arc<TableInstance<E>>, Error<E>> {
diff --git a/src/interpreter/program.rs b/src/interpreter/program.rs
index 1040cb9..f34236e 100644
--- a/src/interpreter/program.rs
+++ b/src/interpreter/program.rs
@@ -67,7 +67,7 @@ impl<E> ProgramInstanceEssence<E> where E: UserError {
 		modules.insert("env".into(), env_module);
 		Ok(ProgramInstanceEssence {
 			modules: RwLock::new(modules),
-		})		
+		})
 	}
 
 	/// Get module reference.