diff --git a/include/xo/arena/AllocHeaderConfig.hpp b/include/xo/arena/AllocHeaderConfig.hpp
index ab56088..d2b6db9 100644
--- a/include/xo/arena/AllocHeaderConfig.hpp
+++ b/include/xo/arena/AllocHeaderConfig.hpp
@@ -11,7 +11,9 @@
 
 namespace xo {
     namespace mm {
-        /*
+        /**
+         * @brief specifies alloc header layout
+         *
          * Each allocation is preceded by a 64-bit header.
          * Header is split into 3 configurable-width bit fields,
          * labelled (from hi to lo bit order) {tseq, age, size}.
@@ -36,7 +38,7 @@ namespace xo {
          *  0..............01111111   gen_mask_unshifted
          *  0..011111110..........0   gen_mask_shifted
          *             >           <  gen_shift
-         */
+         **/
         struct AllocHeaderConfig {
             using repr_type = AllocHeader;
             using span_type = std::pair<const std::byte *, const std::byte *>;
diff --git a/include/xo/arena/DArena.hpp b/include/xo/arena/DArena.hpp
index 83ebd9c..73ca67d 100644
--- a/include/xo/arena/DArena.hpp
+++ b/include/xo/arena/DArena.hpp
@@ -103,6 +103,9 @@ namespace xo {
             /** @defgroup mm-arena-methods **/
             ///@{
 
+            /** false -> not eligible for GC (allocates own memory + not moveable) **/
+            static constexpr bool is_gc_eligible() { return false; }
+
             /** Reserved memory, in bytes. This is the maximum size of this arena. **/
             size_type reserved() const noexcept { return hi_ - lo_; }
             /** Allocated memory in bytes: memory consumed by allocs from this arena,
@@ -125,6 +128,9 @@ namespace xo {
              **/
             bool contains(const void * addr) const noexcept { return (lo_ <= addr) && (addr < hi_); }
 
+            /** Truee iff address @p addr is owned by this arena and in allocated regions **/
+            bool contains_allocated(const void * addr) const noexcept { return (lo_ <= addr) && (addr < free_); }
+
             /** true if arena is mapped i.e. has a reserved address range **/
             bool is_mapped() const noexcept { return (lo_ != nullptr) && (hi_ != nullptr); }
 
@@ -147,6 +153,8 @@ namespace xo {
 
             /** get header from allocated object address **/
             header_type * obj2hdr(void * obj) noexcept;
+            /** get header from allocated object address (const version) **/
+            const header_type * obj2hdr(void * obj) const noexcept;
 
             /** report alloc book-keeping info for allocation at @p mem
              *
diff --git a/include/xo/arena/DArenaHashMap.hpp b/include/xo/arena/DArenaHashMap.hpp
index 50e6669..c97f7ba 100644
--- a/include/xo/arena/DArenaHashMap.hpp
+++ b/include/xo/arena/DArenaHashMap.hpp
@@ -68,6 +68,9 @@ namespace xo {
                           size_type hint_max_capacity = 0,
                           bool debug_flag = false);
 
+            /** true for types that support the AGCObject facet; DArenaHashMap gets its own memory! **/
+            static constexpr bool is_gc_eligible() { return false; }
+
             size_type empty() const noexcept { return store_.empty(); }
             size_type groups() const noexcept { return store_.n_group_; }
             size_type size() const noexcept { return store_.size_; }
diff --git a/include/xo/arena/DArenaVector.hpp b/include/xo/arena/DArenaVector.hpp
index 79653fe..0ac5d68 100644
--- a/include/xo/arena/DArenaVector.hpp
+++ b/include/xo/arena/DArenaVector.hpp
@@ -76,6 +76,7 @@ namespace xo {
             const_iterator cend() const noexcept { return this->_address_of(size_); }
             const_iterator end() const noexcept { return this->cend(); }
 
+            constexpr const DArena * store() const { return &store_; }
             constexpr T * data() { return reinterpret_cast<T*>(store_.lo_); }
             constexpr const T * data() const { return reinterpret_cast<const T*>(store_.lo_); }
 
@@ -223,7 +224,7 @@ namespace xo {
             //
             store_.restore(zero_ckp_);
             store_.alloc(xo::reflect::typeseq::id<std::byte>(), req_z);
-            
+
             this->size_ = z;
         }
 
diff --git a/src/arena/DArena.cpp b/src/arena/DArena.cpp
index 2cd36dc..e5bbb11 100644
--- a/src/arena/DArena.cpp
+++ b/src/arena/DArena.cpp
@@ -170,8 +170,17 @@ namespace xo {
             return (header_type *)((byte *)obj - sizeof(header_type));
         }
 
+        auto
+        DArena::obj2hdr(void * obj) const noexcept -> const header_type *
+        {
+            assert(config_.store_header_flag_);
+
+            return (const header_type *)((byte *)obj - sizeof(header_type));
+        }
+
         void
-        DArena::visit_pools(const MemorySizeVisitor & fn) const {
+        DArena::visit_pools(const MemorySizeVisitor & fn) const
+        {
             /** arena can't tell purpose of allocated memory;
              *  must assume it's all used
              **/