diff --git a/Source/Engine/McBopomofoLM.cpp b/Source/Engine/McBopomofoLM.cpp
index c7b51c49..9c73bcef 100644
--- a/Source/Engine/McBopomofoLM.cpp
+++ b/Source/Engine/McBopomofoLM.cpp
@@ -131,7 +131,7 @@ bool McBopomofoLM::externalConverterEnabled()
     return m_externalConverterEnabled;
 }
 
-void McBopomofoLM::setExternalConvrter(std::function<string(string)> externalConverter)
+void McBopomofoLM::setExternalConverter(std::function<string(string)> externalConverter)
 {
     m_externalConverter = externalConverter;
 }
diff --git a/Source/Engine/McBopomofoLM.h b/Source/Engine/McBopomofoLM.h
index 3b8a5109..de90a4a3 100644
--- a/Source/Engine/McBopomofoLM.h
+++ b/Source/Engine/McBopomofoLM.h
@@ -34,27 +34,74 @@ namespace McBopomofo {
 
 using namespace Formosa::Gramambular;
 
+/// McBopomofoLM is a facade for managing a set of models including
+/// the input method language model, user phrases and excluded phrases.
+///
+/// It is the primary model class that the input controller and grammer builder
+/// of McBopomofo talk to. When the grammer builder starts to build a sentense
+/// from a series of BPMF readings, it passes the readings to the model to see
+/// if there are valid unigrams, and use returned unigrams to produce the final
+/// results.
+///
+/// McBopomofoLM combine and transform the unigrams from the primary language
+/// model and user phrases. The process is
+///
+/// 1) Get the original unigrams.
+/// 2) Drop the unigrams whose value is contained in the exclusion map.
+/// 3) Replace the values of the unigrams using the phrase replacement map.
+/// 4) Replace the values of the unigrams using an external converter lambda.
+/// 5) Drop the duplicated phrases.
+///
+/// The controller can ask the model to load the primary input method language
+/// model while launching and to load the user phrases anytime if the custom
+/// files are modified. It does not keep the reference of the data pathes but
+/// you have to pass the paths when you ask it to do loading.
 class McBopomofoLM : public LanguageModel {
 public:
     McBopomofoLM();
     ~McBopomofoLM();
 
+    /// Asks to load the primary language model a the given path.
+    /// @param languageModelPath Thw path of the language model.
     void loadLanguageModel(const char* languageModelPath);
+    /// Asks to load the user phrases and excluded phrases at the given path.
+    /// @param userPhrasesPath The path of user phrases.
+    /// @param excludedPhrasesPath The path of excluded phrases.
     void loadUserPhrases(const char* userPhrasesPath, const char* excludedPhrasesPath);
+    /// Asks to load th phrase replacement table at the given path.
+    /// @param phraseReplacementPath The path of the phrase replacement table.
     void loadPhraseReplacementMap(const char* phraseReplacementPath);
 
+    /// Not implemented since we do not have data to provide bigram function.
     const vector<Bigram> bigramsForKeys(const string& preceedingKey, const string& key);
+    /// Returns a list of available unigram for the given key.
+    /// @param key A string represents the BPMF reading or a symbol key. For
+    ///     example, it you pass "ㄇㄚ", it returns "嗎", "媽", and so on.
     const vector<Unigram> unigramsForKey(const string& key);
+    /// If the model has unigrams for the given key.
+    /// @param key The key.
     bool hasUnigramsForKey(const string& key);
 
+    /// Enables or disables phrase replacement.
     void setPhraseReplacementEnabled(bool enabled);
+    /// If phrease replacement is enabled or not.
     bool phraseReplacementEnabled();
 
+    /// Enables or disables the external converter.
     void setExternalConverterEnabled(bool enabled);
+    /// If the external converted is enabled or not.
     bool externalConverterEnabled();
-    void setExternalConvrter(std::function<string(string)> externalConverter);
+    /// Sets a lambda to let the values of unigrams could be converted by it.
+    void setExternalConverter(std::function<string(string)> externalConverter);
 
 protected:
+    /// Filters and converts the input unigrams and return a new list of unigrams.
+    /// 
+    /// @param unigrams The unigrams to be processed.
+    /// @param excludedValues The values to excluded unigrams.
+    /// @param insertedValues The values for unigrams already in the results.
+    ///   It helps to prevent duplicated unigrams. Please note that the method
+    ///   has a side effect that it inserts values to `insertedValues`.
     const vector<Unigram> filterAndTransformUnigrams(const vector<Unigram> unigrams,
         const std::unordered_set<string>& excludedValues,
         std::unordered_set<string>& insertedValues);
diff --git a/Source/LanguageModelManager.mm b/Source/LanguageModelManager.mm
index 37fa2897..bdf0ac9f 100644
--- a/Source/LanguageModelManager.mm
+++ b/Source/LanguageModelManager.mm
@@ -68,8 +68,8 @@ static void LTLoadLanguageModelFile(NSString *filenameWithoutExtension, McBopomo
         return string(text.UTF8String);
     };
 
-    gLanguageModelMcBopomofo.setExternalConvrter(converter);
-    gLanguageModelPlainBopomofo.setExternalConvrter(converter);
+    gLanguageModelMcBopomofo.setExternalConverter(converter);
+    gLanguageModelPlainBopomofo.setExternalConverter(converter);
 }
 
 + (BOOL)checkIfUserDataFolderExists