Update NPCs.md

doc/NPCs.md

@@ -770,6 +770,11 @@ One of `"for_item"` or `"for_category"`, and each can either be a single string
 
 ---
 
+## Dialogue State
+Variables and information relevant to the current dialogue can be tracked using `context variables`. Accessing these is discussed further in [variable object](#variable-object).  The main thing that makes context variables special however is that they are only relevant to the current dialogue and any child dialogue / effects. When the dialogue or effect ends any context variables defined inside go out of scope (stop existing).
+
+---
+
 ## Dialogue Effects
 The `effect` field of `speaker_effect` or a `response` can be any of the following effects. Multiple effects should be arranged in a list and are processed in the order listed.
 
@@ -1216,7 +1221,7 @@ Condition | Type | Description
 ## Utility Structures
 
 ### Variable Object
-`variable_object`: This is either an object, an `arithmetic`/`math` [expression](#compare-numbers-and-arithmetics) or array describing a variable name. It can either describe a double, a time duration or a string. If it is an array it must have 2 values the first of which will be a minimum and the second will be a maximum, the value will be randomly between the two. If it is a double `default` is a double which will be the value returned if the variable is not defined. If is it a duration then `default` can be either an int or a string describing a time span. `u_val`, `npc_val`, or `global_val` can be the used for the variable name element.  If `u_val` is used it describes a variable on player u, if `npc_val` is used it describes a variable on player npc, if `global_val` is used it describes a global variable.  If this is a duration `infinite` will be accepted to be a virtually infinite value(it is actually more than a year, if longer is needed a code change to make this a flag or something will be needed).
+`variable_object`: This is either an object, an `arithmetic`/`math` [expression](#compare-numbers-and-arithmetics) or array describing a variable name. It can either describe a double, a time duration or a string. If it is an array it must have 2 values the first of which will be a minimum and the second will be a maximum, the value will be randomly between the two. If it is a double `default` is a double which will be the value returned if the variable is not defined. If is it a duration then `default` can be either an int or a string describing a time span. `u_val`, `npc_val`, `context_val`, or `global_val` can be the used for the variable name element.  If `u_val` is used it describes a variable on player u, if `npc_val` is used it describes a variable on player npc, if `context_val` is used it describes a variable on the current dialogue context, if `global_val` is used it describes a global variable.  If this is a duration `infinite` will be accepted to be a virtually infinite value(it is actually more than a year, if longer is needed a code change to make this a flag or something will be needed).
 
 Example:
 ```json
@@ -1367,7 +1372,7 @@ If `operator` is `==`, `>=`, `<=`, `>`, or `<`, the operation is a comparison:
 `lhs` and `rhs` are evaluated independently and the result of `operator` is passed on to the parent object.
 
 #### Variables
-Tokens that aren't numbers, [constants](#constants), [functions](#math-functions), or mathematical symbols are treated as dialogue variables. They are scoped by their name so `myvar` is a variable in the global scope, `u_myvar` is scoped on the alpha talker, and `n_myvar` is scoped on the beta talker.
+Tokens that aren't numbers, [constants](#constants), [functions](#math-functions), or mathematical symbols are treated as dialogue variables. They are scoped by their name so `myvar` is a variable in the global scope, `u_myvar` is scoped on the alpha talker, `n_myvar` is scoped on the beta talker, and `_var` is a context variable.
 
 Examples:
 ```JSON