diff --git a/abstractattachment.cpp b/abstractattachment.cpp
index e89f605..9d586dd 100644
--- a/abstractattachment.cpp
+++ b/abstractattachment.cpp
@@ -14,6 +14,9 @@ using namespace CppUtilities;
 
 namespace TagParser {
 
+/// \brief The AbstractAttachmentPrivate struct contains private fields of the AbstractAttachment class.
+struct AbstractAttachmentPrivate {};
+
 /*!
  * \class TagParser::StreamDataBlock
  * \brief The StreamDataBlock class is a reference to a certain data block of a stream.
@@ -127,6 +130,23 @@ FileDataBlock::~FileDataBlock()
  * \brief The AbstractAttachment class parses and stores attachment information.
  */
 
+/*!
+ * \brief Constructs a new attachment.
+ */
+AbstractAttachment::AbstractAttachment()
+    : m_id(0)
+    , m_isDataFromFile(false)
+    , m_ignored(false)
+{
+}
+
+/*!
+ * \brief Destroys the attachment.
+ */
+AbstractAttachment::~AbstractAttachment()
+{
+}
+
 /*!
  * \brief Returns a label for the track.
  */
diff --git a/abstractattachment.h b/abstractattachment.h
index 95ade0d..96a77c9 100644
--- a/abstractattachment.h
+++ b/abstractattachment.h
@@ -102,6 +102,8 @@ inline const MediaFileInfo *FileDataBlock::fileInfo() const
     return m_fileInfo.get();
 }
 
+struct AbstractAttachmentPrivate;
+
 class TAG_PARSER_EXPORT AbstractAttachment {
 public:
     const std::string &description() const;
@@ -123,7 +125,8 @@ public:
     bool isEmpty() const;
 
 protected:
-    AbstractAttachment();
+    explicit AbstractAttachment();
+    virtual ~AbstractAttachment();
 
 private:
     std::string m_description;
@@ -131,20 +134,11 @@ private:
     std::string m_mimeType;
     std::uint64_t m_id;
     std::unique_ptr<StreamDataBlock> m_data;
+    std::unique_ptr<AbstractAttachmentPrivate> m_p;
     bool m_isDataFromFile;
     bool m_ignored;
 };
 
-/*!
- * \brief Constructs a new attachment.
- */
-inline AbstractAttachment::AbstractAttachment()
-    : m_id(0)
-    , m_isDataFromFile(false)
-    , m_ignored(false)
-{
-}
-
 /*!
  * \brief Returns a description of the attachment.
  */
diff --git a/abstractchapter.cpp b/abstractchapter.cpp
index e96f53d..aa05126 100644
--- a/abstractchapter.cpp
+++ b/abstractchapter.cpp
@@ -8,6 +8,9 @@ using namespace CppUtilities;
 
 namespace TagParser {
 
+/// \brief The AbstractChapterPrivate struct contains private fields of the AbstractChapter class.
+struct AbstractChapterPrivate {};
+
 /*!
  * \class TagParser::AbstractChapter
  * \brief The AbstractChapter class parses chapter information.
diff --git a/abstractchapter.h b/abstractchapter.h
index a47c645..6ee0ce3 100644
--- a/abstractchapter.h
+++ b/abstractchapter.h
@@ -5,6 +5,7 @@
 
 #include <c++utilities/chrono/timespan.h>
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -12,6 +13,7 @@ namespace TagParser {
 
 class AbortableProgressFeedback;
 class Diagnostics;
+struct AbstractChapterPrivate;
 
 class TAG_PARSER_EXPORT AbstractChapter {
 public:
@@ -41,6 +43,7 @@ protected:
     CppUtilities::TimeSpan m_startTime;
     CppUtilities::TimeSpan m_endTime;
     std::vector<std::uint64_t> m_tracks;
+    std::unique_ptr<AbstractChapterPrivate> m_p;
     bool m_hidden;
     bool m_enabled;
 };
diff --git a/abstractcontainer.cpp b/abstractcontainer.cpp
index 9cd2bfc..cbd2723 100644
--- a/abstractcontainer.cpp
+++ b/abstractcontainer.cpp
@@ -6,6 +6,9 @@ using namespace CppUtilities;
 
 namespace TagParser {
 
+/// \brief The AbstractContainerPrivate struct contains private fields of the AbstractContainer class.
+struct AbstractContainerPrivate {};
+
 /*!
  * \class TagParser::AbstractContainer
  * \brief The AbstractContainer class provides an interface and common functionality to parse and make a certain container format.
diff --git a/abstractcontainer.h b/abstractcontainer.h
index 1b53806..db7e5bf 100644
--- a/abstractcontainer.h
+++ b/abstractcontainer.h
@@ -11,6 +11,7 @@
 #include <c++utilities/io/binarywriter.h>
 
 #include <iostream>
+#include <memory>
 
 namespace CppUtilities {
 class BinaryReader;
@@ -25,6 +26,7 @@ class AbstractChapter;
 class AbstractAttachment;
 class Diagnostics;
 class AbortableProgressFeedback;
+struct AbstractContainerPrivate;
 
 class TAG_PARSER_EXPORT AbstractContainer {
 public:
@@ -119,6 +121,7 @@ private:
     std::iostream *m_stream;
     CppUtilities::BinaryReader m_reader;
     CppUtilities::BinaryWriter m_writer;
+    std::unique_ptr<AbstractContainerPrivate> m_p;
 };
 
 /*!
diff --git a/abstracttrack.cpp b/abstracttrack.cpp
index b959f43..800877c 100644
--- a/abstracttrack.cpp
+++ b/abstracttrack.cpp
@@ -11,6 +11,9 @@ using namespace CppUtilities;
 
 namespace TagParser {
 
+/// \brief The AbstractTrackPrivate struct contains private fields of the AbstractTrack class.
+struct AbstractTrackPrivate {};
+
 /*!
  * \class TagParser::AbstractTrack
  * \brief The AbstractTrack class parses and stores technical information about
diff --git a/abstracttrack.h b/abstracttrack.h
index 9b38d4d..249141a 100644
--- a/abstracttrack.h
+++ b/abstracttrack.h
@@ -15,6 +15,7 @@
 #include <c++utilities/misc/flagenumclass.h>
 
 #include <iosfwd>
+#include <memory>
 #include <string>
 #include <string_view>
 
@@ -104,6 +105,8 @@ CPP_UTILITIES_MARK_FLAG_ENUM_CLASS(TagParser, TagParser::TrackFlags)
 
 namespace TagParser {
 
+struct AbstractTrackPrivate;
+
 class TAG_PARSER_EXPORT AbstractTrack {
     friend class MpegAudioFrameStream;
     friend class WaveAudioStream;
@@ -232,6 +235,7 @@ protected:
     AlphaMode m_alphaMode;
     DisplayUnit m_displayUnit;
     AspectRatioType m_aspectRatioType;
+    std::unique_ptr<AbstractTrackPrivate> m_p;
 
 private:
     std::string makeDescription(bool verbose) const;
diff --git a/mediafileinfo.cpp b/mediafileinfo.cpp
index 407f81d..112c13e 100644
--- a/mediafileinfo.cpp
+++ b/mediafileinfo.cpp
@@ -59,6 +59,9 @@ using namespace CppUtilities;
 
 namespace TagParser {
 
+/// \brief The MediaFileInfoPrivate struct contains private fields of the MediaFileInfo class.
+struct MediaFileInfoPrivate {};
+
 /*!
  * \class TagParser::MediaFileInfo
  * \brief The MediaFileInfo class allows to read and write tag information providing
diff --git a/mediafileinfo.h b/mediafileinfo.h
index 4fa5ba8..80d068b 100644
--- a/mediafileinfo.h
+++ b/mediafileinfo.h
@@ -73,6 +73,8 @@ CPP_UTILITIES_MARK_FLAG_ENUM_CLASS(TagParser, TagParser::MediaFileHandlingFlags)
 
 namespace TagParser {
 
+struct MediaFileInfoPrivate;
+
 class TAG_PARSER_EXPORT MediaFileInfo : public BasicFileInfo {
 public:
     // constructor, destructor
@@ -226,6 +228,7 @@ private:
     ElementPosition m_tagPosition;
     ElementPosition m_indexPosition;
     MediaFileHandlingFlags m_fileHandlingFlags;
+    std::unique_ptr<MediaFileInfoPrivate> m_p;
 };
 
 /*!
diff --git a/tag.cpp b/tag.cpp
index c995ed2..5701109 100644
--- a/tag.cpp
+++ b/tag.cpp
@@ -4,6 +4,9 @@ using namespace std;
 
 namespace TagParser {
 
+/// \brief The TagPrivate struct contains private fields of the Tag class.
+struct TagPrivate {};
+
 /*!
  * \class TagParser::Tag
  * \brief The Tag class is used to store, read and write tag information.
diff --git a/tag.h b/tag.h
index 587e33a..5fe6c51 100644
--- a/tag.h
+++ b/tag.h
@@ -8,6 +8,7 @@
 #include <c++utilities/io/binaryreader.h>
 
 #include <cstdint>
+#include <memory>
 #include <string>
 #include <type_traits>
 
@@ -160,6 +161,8 @@ constexpr KnownField nextKnownField(KnownField field)
     return isKnownFieldDeprecated(next) ? nextKnownField(next) : next;
 }
 
+struct TagPrivate;
+
 class TAG_PARSER_EXPORT Tag {
 public:
     virtual ~Tag();
@@ -199,6 +202,7 @@ protected:
 
     std::string m_version;
     std::uint64_t m_size;
+    std::unique_ptr<TagPrivate> m_p;
     TagTarget m_target;
 };
 
diff --git a/tagvalue.cpp b/tagvalue.cpp
index fd9c26c..eab61ff 100644
--- a/tagvalue.cpp
+++ b/tagvalue.cpp
@@ -22,6 +22,9 @@ using namespace CppUtilities;
 
 namespace TagParser {
 
+/// \brief The TagValuePrivate struct contains private fields of the TagValue class.
+struct TagValuePrivate {};
+
 /*!
  * \brief Returns the string representation of the specified \a dataType.
  */
@@ -145,6 +148,140 @@ TagValue::TagValue(const TagValue &other)
     }
 }
 
+TagValue::TagValue(TagValue &&other) = default;
+
+/*!
+ * \brief Constructs an empty TagValue.
+ */
+TagValue::TagValue()
+    : m_size(0)
+    , m_type(TagDataType::Undefined)
+    , m_encoding(TagTextEncoding::Latin1)
+    , m_descEncoding(TagTextEncoding::Latin1)
+    , m_flags(TagValueFlags::None)
+{
+}
+
+/*!
+ * \brief Constructs a new TagValue holding a copy of the given \a text.
+ * \param text Specifies the text to be assigned.
+ * \param textSize Specifies the size of \a text. (The actual number of bytes, not the number of characters.)
+ * \param textEncoding Specifies the encoding of the given \a text.
+ * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
+ *                  use \a textEncoding without any character set conversions.
+ * \throws Throws a ConversionException if the conversion the specified character set fails.
+ * \remarks Strips the BOM of the specified \a text.
+ */
+TagValue::TagValue(const char *text, std::size_t textSize, TagTextEncoding textEncoding, TagTextEncoding convertTo)
+    : m_descEncoding(TagTextEncoding::Latin1)
+    , m_flags(TagValueFlags::None)
+{
+    assignText(text, textSize, textEncoding, convertTo);
+}
+
+/*!
+ * \brief Constructs a new TagValue holding a copy of the given \a text.
+ * \param text Specifies the text to be assigned. This string must be null-terminated.
+ * \param textEncoding Specifies the encoding of the given \a text.
+ * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
+ *                  use \a textEncoding without any character set conversions.
+ * \throws Throws a ConversionException if the conversion the specified character set fails.
+ * \remarks Strips the BOM of the specified \a text.
+ */
+TagValue::TagValue(const char *text, TagTextEncoding textEncoding, TagTextEncoding convertTo)
+{
+    assignText(text, std::strlen(text), textEncoding, convertTo);
+}
+
+/*!
+ * \brief Constructs a new TagValue holding a copy of the given \a text.
+ * \param text Specifies the text to be assigned.
+ * \param textEncoding Specifies the encoding of the given \a text.
+ * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
+ *                  use \a textEncoding without any character set conversions.
+ * \throws Throws a ConversionException if the conversion the specified character set fails.
+ * \remarks Strips the BOM of the specified \a text.
+ */
+TagValue::TagValue(const std::string &text, TagTextEncoding textEncoding, TagTextEncoding convertTo)
+    : m_descEncoding(TagTextEncoding::Latin1)
+    , m_flags(TagValueFlags::None)
+{
+    assignText(text, textEncoding, convertTo);
+}
+
+/*!
+ * \brief Constructs a new TagValue holding a copy of the given \a text.
+ * \param text Specifies the text to be assigned.
+ * \param textEncoding Specifies the encoding of the given \a text.
+ * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
+ *                  use \a textEncoding without any character set conversions.
+ * \throws Throws a ConversionException if the conversion the specified character set fails.
+ * \remarks Strips the BOM of the specified \a text.
+ */
+TagValue::TagValue(std::string_view text, TagTextEncoding textEncoding, TagTextEncoding convertTo)
+    : m_descEncoding(TagTextEncoding::Latin1)
+    , m_flags(TagValueFlags::None)
+{
+    assignText(text, textEncoding, convertTo);
+}
+
+/*!
+ * \brief Destroys the TagValue.
+ */
+TagValue::~TagValue()
+{
+}
+
+/*!
+ * \brief Constructs a new TagValue with a copy of the given \a data.
+ *
+ * \param data Specifies a pointer to the data.
+ * \param length Specifies the length of the data.
+ * \param type Specifies the type of the data as TagDataType.
+ * \param encoding Specifies the encoding of the data as TagTextEncoding. The
+ *                 encoding will only be considered if a text is assigned.
+ * \remarks Strips the BOM of the specified \a data if \a type is TagDataType::Text.
+ */
+TagValue::TagValue(const char *data, std::size_t length, TagDataType type, TagTextEncoding encoding)
+    : m_size(length)
+    , m_type(type)
+    , m_encoding(encoding)
+    , m_descEncoding(TagTextEncoding::Latin1)
+    , m_flags(TagValueFlags::None)
+{
+    if (length) {
+        if (type == TagDataType::Text) {
+            stripBom(data, m_size, encoding);
+        }
+        m_ptr = std::make_unique<char[]>(m_size);
+        std::copy(data, data + m_size, m_ptr.get());
+    }
+}
+
+/*!
+ * \brief Constructs a new TagValue holding with the given \a data.
+ *
+ * The \a data is not copied. It is moved.
+ *
+ * \param data Specifies a pointer to the data.
+ * \param length Specifies the length of the data.
+ * \param type Specifies the type of the data as TagDataType.
+ * \param encoding Specifies the encoding of the data as TagTextEncoding. The
+ *                 encoding will only be considered if a text is assigned.
+ * \remarks Does not strip the BOM so for consistency the caller must ensure there is no BOM present.
+ */
+TagValue::TagValue(std::unique_ptr<char[]> &&data, std::size_t length, TagDataType type, TagTextEncoding encoding)
+    : m_size(length)
+    , m_type(type)
+    , m_encoding(encoding)
+    , m_descEncoding(TagTextEncoding::Latin1)
+    , m_flags(TagValueFlags::None)
+{
+    if (length) {
+        m_ptr = std::move(data);
+    }
+}
+
 /*!
  * \brief Assigns the value of another TagValue to the current instance.
  */
@@ -170,6 +307,8 @@ TagValue &TagValue::operator=(const TagValue &other)
     return *this;
 }
 
+TagValue &TagValue::operator=(TagValue &&other) = default;
+
 /// \cond
 TagTextEncoding pickUtfEncoding(TagTextEncoding encoding1, TagTextEncoding encoding2)
 {
diff --git a/tagvalue.h b/tagvalue.h
index 1f57ddf..7b540d1 100644
--- a/tagvalue.h
+++ b/tagvalue.h
@@ -140,6 +140,8 @@ enum class TagValueComparisionFlags : unsigned int {
     IgnoreMetaData = 0x2, /**< do *not* take meta-data like description and MIME-types into account */
 };
 
+struct TagValuePrivate;
+
 class TAG_PARSER_EXPORT TagValue {
 public:
     // constructor, destructor
@@ -164,12 +166,12 @@ public:
     explicit TagValue(CppUtilities::TimeSpan value);
     explicit TagValue(const Popularity &value);
     TagValue(const TagValue &other);
-    TagValue(TagValue &&other) = default;
+    TagValue(TagValue &&other);
     ~TagValue();
 
     // operators
     TagValue &operator=(const TagValue &other);
-    TagValue &operator=(TagValue &&other) = default;
+    TagValue &operator=(TagValue &&other);
     bool operator==(const TagValue &other) const;
     bool operator!=(const TagValue &other) const;
     operator bool() const;
@@ -260,90 +262,9 @@ private:
     TagTextEncoding m_encoding;
     TagTextEncoding m_descEncoding;
     TagValueFlags m_flags;
+    std::unique_ptr<TagValuePrivate> m_p;
 };
 
-/*!
- * \brief Constructs an empty TagValue.
- */
-inline TagValue::TagValue()
-    : m_size(0)
-    , m_type(TagDataType::Undefined)
-    , m_encoding(TagTextEncoding::Latin1)
-    , m_descEncoding(TagTextEncoding::Latin1)
-    , m_flags(TagValueFlags::None)
-{
-}
-
-/*!
- * \brief Destroys the TagValue.
- */
-inline TagValue::~TagValue()
-{
-}
-
-/*!
- * \brief Constructs a new TagValue holding a copy of the given \a text.
- * \param text Specifies the text to be assigned.
- * \param textSize Specifies the size of \a text. (The actual number of bytes, not the number of characters.)
- * \param textEncoding Specifies the encoding of the given \a text.
- * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
- *                  use \a textEncoding without any character set conversions.
- * \throws Throws a ConversionException if the conversion the specified character set fails.
- * \remarks Strips the BOM of the specified \a text.
- */
-inline TagValue::TagValue(const char *text, std::size_t textSize, TagTextEncoding textEncoding, TagTextEncoding convertTo)
-    : m_descEncoding(TagTextEncoding::Latin1)
-    , m_flags(TagValueFlags::None)
-{
-    assignText(text, textSize, textEncoding, convertTo);
-}
-
-/*!
- * \brief Constructs a new TagValue holding a copy of the given \a text.
- * \param text Specifies the text to be assigned. This string must be null-terminated.
- * \param textEncoding Specifies the encoding of the given \a text.
- * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
- *                  use \a textEncoding without any character set conversions.
- * \throws Throws a ConversionException if the conversion the specified character set fails.
- * \remarks Strips the BOM of the specified \a text.
- */
-inline TagValue::TagValue(const char *text, TagTextEncoding textEncoding, TagTextEncoding convertTo)
-{
-    assignText(text, std::strlen(text), textEncoding, convertTo);
-}
-
-/*!
- * \brief Constructs a new TagValue holding a copy of the given \a text.
- * \param text Specifies the text to be assigned.
- * \param textEncoding Specifies the encoding of the given \a text.
- * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
- *                  use \a textEncoding without any character set conversions.
- * \throws Throws a ConversionException if the conversion the specified character set fails.
- * \remarks Strips the BOM of the specified \a text.
- */
-inline TagValue::TagValue(const std::string &text, TagTextEncoding textEncoding, TagTextEncoding convertTo)
-    : m_descEncoding(TagTextEncoding::Latin1)
-    , m_flags(TagValueFlags::None)
-{
-    assignText(text, textEncoding, convertTo);
-}
-
-/*!
- * \brief Constructs a new TagValue holding a copy of the given \a text.
- * \param text Specifies the text to be assigned.
- * \param textEncoding Specifies the encoding of the given \a text.
- * \param convertTo Specifies the encoding to convert \a text to; set to TagTextEncoding::Unspecified to
- *                  use \a textEncoding without any character set conversions.
- * \throws Throws a ConversionException if the conversion the specified character set fails.
- * \remarks Strips the BOM of the specified \a text.
- */
-inline TagValue::TagValue(std::string_view text, TagTextEncoding textEncoding, TagTextEncoding convertTo)
-    : m_descEncoding(TagTextEncoding::Latin1)
-    , m_flags(TagValueFlags::None)
-{
-    assignText(text, textEncoding, convertTo);
-}
-
 /*!
  * \brief Constructs a new TagValue holding the given integer \a value.
  */
@@ -360,56 +281,6 @@ inline TagParser::TagValue::TagValue(std::uint64_t value)
 {
 }
 
-/*!
- * \brief Constructs a new TagValue with a copy of the given \a data.
- *
- * \param data Specifies a pointer to the data.
- * \param length Specifies the length of the data.
- * \param type Specifies the type of the data as TagDataType.
- * \param encoding Specifies the encoding of the data as TagTextEncoding. The
- *                 encoding will only be considered if a text is assigned.
- * \remarks Strips the BOM of the specified \a data if \a type is TagDataType::Text.
- */
-inline TagValue::TagValue(const char *data, std::size_t length, TagDataType type, TagTextEncoding encoding)
-    : m_size(length)
-    , m_type(type)
-    , m_encoding(encoding)
-    , m_descEncoding(TagTextEncoding::Latin1)
-    , m_flags(TagValueFlags::None)
-{
-    if (length) {
-        if (type == TagDataType::Text) {
-            stripBom(data, m_size, encoding);
-        }
-        m_ptr = std::make_unique<char[]>(m_size);
-        std::copy(data, data + m_size, m_ptr.get());
-    }
-}
-
-/*!
- * \brief Constructs a new TagValue holding with the given \a data.
- *
- * The \a data is not copied. It is moved.
- *
- * \param data Specifies a pointer to the data.
- * \param length Specifies the length of the data.
- * \param type Specifies the type of the data as TagDataType.
- * \param encoding Specifies the encoding of the data as TagTextEncoding. The
- *                 encoding will only be considered if a text is assigned.
- * \remarks Does not strip the BOM so for consistency the caller must ensure there is no BOM present.
- */
-inline TagValue::TagValue(std::unique_ptr<char[]> &&data, std::size_t length, TagDataType type, TagTextEncoding encoding)
-    : m_size(length)
-    , m_type(type)
-    , m_encoding(encoding)
-    , m_descEncoding(TagTextEncoding::Latin1)
-    , m_flags(TagValueFlags::None)
-{
-    if (length) {
-        m_ptr = std::move(data);
-    }
-}
-
 /*!
  * \brief Constructs a new TagValue holding a copy of the given PositionInSet \a value.
  */