diff --git a/internal_nodefunctions.lua b/internal_nodefunctions.lua
new file mode 100644
index 0000000..a9ee95b
--- /dev/null
+++ b/internal_nodefunctions.lua
@@ -0,0 +1,102 @@
+local function remove_timer(pos)
+    local t = minetest.get_node_timer(pos)
+    t:stop()
+end
+
+function yl_api_nodestages.remove_timer(pos) return remove_timer(pos) end
+
+function yl_api_nodestages.on_destruct(pos) return remove_timer(pos) end
+
+local function on_construct(pos)
+    local node = minetest.get_node(pos)
+    local nodename = node.name
+    local stage = minetest.registered_nodes[nodename]._stage
+    local duration = stage.duration or 0
+
+    if (duration > 0) then
+        local current_duration = duration
+        local t = minetest.get_node_timer(pos)
+        t:start(current_duration)
+    end
+end
+
+function yl_api_nodestages.on_construct(pos) return on_construct(pos) end
+
+local function get_target_nodename(node, pos, next_stages)
+    local sum = 0
+    for _, stage_chance in pairs(next_stages) do sum = sum + stage_chance[2] end
+    local dice = math.random(sum)
+    for _, stage_chance in pairs(next_stages) do
+        dice = dice - stage_chance[2]
+        if dice <= 0 then
+            if (minetest.registered_nodes[stage_chance[1]] == nil) then
+                minetest.log("warning",
+                             yl_api_nodestages.t(
+                                 "target_nodestage_does_not_exist",
+                                 dump(stage_chance[1]), dump(node.name),
+                                 dump(pos)))
+                return nil
+            elseif ((stage_chance[3] ~= nil) and
+                (type(stage_chance[3].can_set) == "function") and
+                (stage_chance[3].can_set(pos) == false)) then
+                return node.name
+            else
+                return stage_chance[1]
+            end
+        end
+    end
+
+    -- should never return this
+    return yl_api_nodestages.error
+end
+
+local function on_timer(pos, elapsed)
+
+    local node = minetest.get_node(pos)
+
+    local stage = minetest.registered_nodes[node.name]._stage
+    local target_nodename
+    local timer = 0
+    local duration
+
+    if ((stage == nil) or (stage.next_stages == nil) or (stage.duration == nil)) then
+        yl_api_nodestages.remove_timer(pos)
+        return
+    end
+
+    repeat
+        duration = stage.duration
+        timer = timer + duration
+        target_nodename = get_target_nodename(node, pos, stage.next_stages)
+
+        if (target_nodename == yl_api_nodestages.error) then
+            -- Thing kaputt, stop it.
+            minetest.log("error", yl_api_nodestages.t("undefined_state_abort"))
+            yl_api_nodestages.remove_timer(pos)
+            return
+        end
+
+        if (target_nodename == nil) then
+            -- Fallback to last known target_nodename
+            target_nodename = stage.stage_name
+            break
+        else
+            -- Last stage most often does not have a _stage
+            stage = minetest.registered_nodes[target_nodename] and
+                        minetest.registered_nodes[target_nodename]._stage or nil
+        end
+    until ((timer >= elapsed) or (stage == nil) or (stage.duration == 0) or (stage.duration == nil))
+
+    if (node.name == target_nodename) then
+        return true end
+
+    minetest.set_node(pos, {name = target_nodename})
+
+    local remaining = timer - elapsed
+    if (stage and stage.duration and (remaining > 0)) then
+        local nodetimer = minetest.get_node_timer(pos)
+        nodetimer:set(stage.duration, remaining)
+    end
+end
+
+function yl_api_nodestages.on_timer(pos, elapsed) return on_timer(pos, elapsed) end
diff --git a/internal_validation.lua b/internal_validation.lua
new file mode 100644
index 0000000..df61266
--- /dev/null
+++ b/internal_validation.lua
@@ -0,0 +1,74 @@
+-- Validation
+--
+
+function get_valid_copy_of_stage(stage)
+    if (type(stage) ~= "table") then return false, t("stage_not_table") end
+
+    local stage = table.copy(stage)
+
+    if (yl_api_nodestages.is_valid_stage(stage) == false) then
+        return false, t("stage_not_valid")
+    end
+
+    return true, stage
+
+end
+
+function yl_api_nodestages.get_valid_copy_of_stage(stage)
+    return get_valid_copy_of_stage(stage)
+end
+
+local function is_valid_stage(stage)
+
+    if (stage == nil) then return false, t("node_does_not_have_stage") end
+
+    if (type(stage) ~= "table") then return false, t("stage_not_table") end
+
+
+
+    return true -- TODO: Implement validation
+end
+
+function yl_api_nodestages.is_valid_stage(stage)
+    return is_valid_stage(stage)
+end
+
+function yl_api_nodestages.is_valid(stages)
+
+    local good, bad, total = 0, 0, 0
+    local reasons = {}
+
+    for _, stage in ipairs(stages) do
+        total = total + 1
+        local success, message = is_valid_stage(stage)
+        if (success == true) then
+            good = good + 1
+        else
+            bad = bad + 1
+            table.insert(reasons, message)
+        end
+    end
+
+    if (bad == 0) then
+        minetest.log("action",
+                     "[MOD] yl_api_nodestages : bad = " .. tostring(bad) ..
+                         ", good = " .. tostring(good) .. ", total = " ..
+                         tostring(total))
+        return true, good, bad, total, reasons
+    else
+        minetest.log("warning",
+                     "[MOD] yl_api_nodestages : bad = " .. tostring(bad) ..
+                         ", good = " .. tostring(good) .. ", total = " ..
+                         tostring(total))
+        return false, good, bad, total, reasons
+    end
+end
+
+function yl_api_nodestages.validate_all_stages()
+    local stages = {}
+    for _, def in pairs(minetest.registered_nodes) do
+        local stage = def._stage
+        table.insert(stages, stage)
+    end
+    return yl_api_nodestages.is_valid(stages)
+end