diff --git a/furvm/include/furvm/thing.hpp b/furvm/include/furvm/thing.hpp
index 9a2c1d9..16dfb98 100644
--- a/furvm/include/furvm/thing.hpp
+++ b/furvm/include/furvm/thing.hpp
@@ -19,10 +19,10 @@ enum class thing_t : std::uint8_t {
 };
 
 /**
- * @brief Returns data size of a thing.
+ * @brief Returns how many bytes a thing would take up.
  *
  * @param type Type of the thing.
- * @return The data size of the thing.
+ * @return The byte count.
  */
 static inline std::size_t thing_type_size(thing_t type) {
     switch (type) {
@@ -35,13 +35,22 @@ template <template <typename> typename Allocator>
 class thing final {
     friend class executor;
 public:
-    using allocator_type = Allocator<std::byte>;
+    using allocator_type = Allocator<std::byte>; /**< Allocator type. */
 public:
+    /**
+     * @brief Constructs a thing.
+     *
+     * @param type Type of the thing.
+     * @param allocator Allocator for the thing's data.
+     */
     thing(thing_t type, const allocator_type& allocator = {})
       : m_type(type), m_allocator(allocator) {
         m_data = m_allocator.allocate(thing_type_size(type));
     }
 
+    /**
+     * @brief Destructs a thing.
+     */
     ~thing() {
         if (m_data != nullptr) m_allocator.deallocate(m_data, thing_type_size(thing_t::Int32));
     }
@@ -74,8 +83,7 @@ public:
     /**
      * @brief Returns a clone of the thing.
      *
-     * @param thing Thing to clone.
-     * @return Shared pointer to a clone of the thing.
+     * @return A clone of this thing.
      */
     thing clone() const {
         class thing res(m_type, m_allocator);
@@ -88,7 +96,7 @@ public:
     }
 public:
     /**
-     * @brief Returns an int32 value from this thing.
+     * @brief Returns the thing's int32 value.
      *
      * @return The value.
      */
@@ -98,7 +106,7 @@ public:
     }
 
     /**
-     * @brief Returns an int32 value from this thing.
+     * @brief Returns the thing's int32 value.
      *
      * @return The value.
      */
@@ -107,66 +115,132 @@ public:
         return *reinterpret_cast<std::int32_t*>(m_data);
     }
 public:
+    /**
+     * @brief Returns a sum of two things.
+     *
+     * @param rhs Thing to sum with this thing (right-hand-side).
+     * @return The sum.
+     */
     thing add(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() + rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Returns a difference of two things.
+     *
+     * @param rhs Thing to subtract from this thing (right-hand-side).
+     * @return The sum.
+     */
     thing sub(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() - rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Returns a product of two things.
+     *
+     * @param rhs Thing to multiply with this thing (right-hand-side).
+     * @return The product.
+     */
     thing mul(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() * rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Returns a quotient of two things.
+     *
+     * @param rhs Thing to divide this thing by (right-hand-side).
+     * @return The quotient.
+     */
     thing div(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() / rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Returns a remainder of two things.
+     *
+     * @param rhs Thing to divide this thing by (right-hand-side).
+     * @return The remainder.
+     */
     thing mod(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() % rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Compares two things for equality.
+     *
+     * @param rhs Thing to compare this thing with (right-hand-side).
+     * @return A boolean result of the comparison in a thing form.
+     */
     thing equals(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() == rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Compares two things for inequality.
+     *
+     * @param rhs Thing to compare this thing with (right-hand-side).
+     * @return A boolean result of the comparison in a thing form.
+     */
     thing not_equals(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() != rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Compares if this thing is less than an another thing.
+     *
+     * @param rhs The another thing.
+     * @return A boolean result of the comparison in a thing form.
+     */
     thing less_than(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() < rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Compares if this thing is greater than an another thing.
+     *
+     * @param rhs The another thing.
+     * @return A boolean result of the comparison in a thing form.
+     */
     thing greater_than(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() > rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Compares if this thing is less than or equal to an another thing.
+     *
+     * @param rhs The another thing.
+     * @return A boolean result of the comparison in a thing form.
+     */
     thing less_equals(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() <= rhs.int32();
         return res;
     }
 
+    /**
+     * @brief Compares if this thing is greater than or equal to an another thing.
+     *
+     * @param rhs The another thing.
+     * @return A boolean result of the comparison in a thing form.
+     */
     thing greater_equals(const thing& rhs) const {
         thing res(m_type, m_allocator);
         res.int32() = int32() >= rhs.int32();
@@ -186,27 +260,26 @@ class thing_allocator {
 
     using dead_things = std::vector<std::pair<T*, std::size_t>>;
 public:
-    using value_type = T;
+    using value_type = T; /**< Value type. */
 public:
+    /**
+     * @brief Constructs a thing allocator.
+     *
+     * @param arena Base arena allocator.
+     */
     explicit thing_allocator(furlang::arena& arena) noexcept
       : m_arena(&arena), m_deadThings(std::make_shared<dead_things>()) {}
 
-    template <typename U>
-    thing_allocator(const thing_allocator<U>& other) noexcept
-      : m_arena(other.m_arena), m_deadThings(other.m_deadThings) {}
-
-    template <typename U>
-    thing_allocator& operator=(const thing_allocator<U>& other) noexcept {
-        if (this == &other) return *this;
-        m_arena      = other.m_arena;
-        m_deadThings = other.m_deadThings;
-        return *this;
-    }
-
+    /**
+     * @brief Move constructor.
+     */
     template <typename U>
     thing_allocator(thing_allocator<U>&& other) noexcept
       : m_arena(std::move(other.m_arena)), m_deadThings(std::move(other.m_deadThings)) {}
 
+    /**
+     * @brief Move constructor.
+     */
     template <typename U>
     thing_allocator& operator=(thing_allocator<U>&& other) noexcept {
         if (this == &other) return *this;
@@ -214,7 +287,31 @@ public:
         m_deadThings = std::move(other.m_deadThings);
         return *this;
     }
+
+    /**
+     * @brief Copy constructor.
+     */
+    template <typename U>
+    thing_allocator(const thing_allocator<U>& other) noexcept
+      : m_arena(other.m_arena), m_deadThings(other.m_deadThings) {}
+
+    /**
+     * @brief Copy constructor.
+     */
+    template <typename U>
+    thing_allocator& operator=(const thing_allocator<U>& other) noexcept {
+        if (this == &other) return *this;
+        m_arena      = other.m_arena;
+        m_deadThings = other.m_deadThings;
+        return *this;
+    }
 public:
+    /**
+     * @brief Returns a free chunk of memory.
+     *
+     * @param count Count of the things that must fit inside the chunk.
+     * @return The chunk.
+     */
     [[nodiscard]] T* allocate(std::size_t count = 1) {
         for (auto it = m_deadThings->begin(); it != m_deadThings->end(); ++it) {
             if (it->second != count) continue;
@@ -224,13 +321,26 @@ public:
         return m_arena->allocate<T>(count);
     }
 
+    /**
+     * @brief Recycles the pointer.
+     */
     void deallocate(T* ptr, std::size_t count) noexcept { m_deadThings->emplace_back(ptr, count); }
 public:
+    /**
+     * @brief Compares two thing allocators for equality.
+     *
+     * @return true if the two things are equal.
+     */
     template <typename U>
     bool operator==(const thing_allocator<U>& other) const noexcept {
         return m_arena == other.m_arena && m_deadThings == other.m_deadThings;
     }
 
+    /**
+     * @brief Compares two thing allocators for inequality.
+     *
+     * @return true if the two things are not equal.
+     */
     template <typename U>
     bool operator!=(const thing_allocator<U>& other) const noexcept {
         return m_arena != other.m_arena || m_deadThings != other.m_deadThings;