started backguard tips page

en/backporting/minetest-engine-api.md

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+### reason or PlayerHPChangeReason
+
+PlayerHPChangeReason table kind of, the minetest api is so crap that does not specified that has properties.. neither refers to the `PlayerHPChangeReason` object, the most important things here are:
+
+> **since** 5.0
+
+* `from` with values of
+    * `mod`
+    * `engine`
+* `type` values when specific hp actions, and also any of those will have additional fields from mods.
+    * `set_hp`: A mod or the engine called set_hp without giving a type - use this for custom damage types.
+    * `punch`: Was punched. reason.object will hold the puncher, or nil if none.
+    * `fall`: the player dies from a high fall or something forced
+    * `node_damage`: `damage_per_second` from a neighboring node. for older 5.2 use the position of player to get `node_pos`
+    * `drown`: **since 5.5**
+    * `respawn`:
+* `node`  **since 5.3** will hold the node name or nil if `type` is `node_damage`. 
+* `node_pos` **since 5.3** will hold the position of the node if `type` is `node_damage`.
+
+### register_on_dieplayer and register_on_player_hpchange
+
+Those functions for player dead were enhanced since version 5, using new [reason or PlayerHPChangeReason](#reason-or-playerhpchangereason)
+
+* `minetest.register_on_dieplayer(function(ObjectRef))` **since 0.4.15, 4.0**
+* `minetest.register_on_dieplayer(function(ObjectRef, reason))` **since 5.0**
+
+Those functions ofr player hp change where enhanced since version 5
+
+* `minetest.register_on_player_hpchange(func(player, hp_change), modifier)` **since 0.4.15, 4.0**
+* `minetest.register_on_player_hpchange(function(player, hp_change, reason), modifier)` **since 5.0**
+