Add documentation on the resolve functions

1 files changed, 12 insertions, 2 deletions

diff --git a/docs/profiles/getting_a_setting_value.md b/docs/profiles/getting_a_setting_value.md
index beb8c38783..4dff6f7aa3 100644
--- a/docs/profiles/getting_a_setting_value.md
+++ b/docs/profiles/getting_a_setting_value.md
@@ -12,8 +12,18 @@ Settings where the `settable_per_mesh` property is false will not be shown in Cu
 
 The per-object settings are stored in a separate container stack that is particular to the object. The container stack is added to the object via a scene decorator. It has just a single container in it, which contains all of the settings that the user changed.
 
+Resolve
+----
+If the setting is not listed in the per-object settings, it needs to be evaluated from the main settings list. However before evaluating it from a particular extruder, Cura will check if the setting has the `resolve` property. If it does, it returns the output of the `resolve` property and that's everything.
+
+The `resolve` property is intended for settings which are global in nature, but still need to be influenced by extruder-specific settings. A good example is the Build Plate Temperature, which is very dependent on the material(s) used by the printer, but there can only be a single bed temperature at a time.
+
+Cura will simply evaluate the `resolve` setting if present, which is an arbitrary Python expression, and return its result as the setting's value. However typically the `resolve` property is a function that takes the values of this setting for all extruders in use and then computes a result based on those. There is a built-in function for that called `extruderValues()`, which returns a list of setting values, one for each extruder. The function can then for instance take the average of those. In the case of the build plate temperature it will take the highest of those. In the case of the adhesion type it will choose "raft" if any extruder uses a raft, or "brim" as second choice, "skirt" as third choice and "none" only if all extruders use "none". Each setting with a `resolve` property has its own way of resolving the setting. The `extruderValues()` function continues with the algorithm as written below, but repeats it for each extruder.
+
 Limit To Extruder
 ----
-If the setting is not listed in the per-object settings, it needs to be evaluated from the extruder that the object is assigned to. However there are some exceptions. Some groups of settings belong to a particular "extruder setting", like the Infill Extruder setting, or the Support Extruder setting. Which extruder a setting belongs to is stored in the `limit_to_extruder` property. Settings which have their `limit_to_extruder` property set to `adhesion_extruder_nr`, for instance, belong to the build plate adhesion settings.
+If a setting is evaluated from a particular extruder stack, it normally gets evaluated from the extruder that the object is assigned to. However there are some exceptions. Some groups of settings belong to a particular "extruder setting", like the Infill Extruder setting, or the Support Extruder setting. Which extruder a setting belongs to is stored in the `limit_to_extruder` property. Settings which have their `limit_to_extruder` property set to `adhesion_extruder_nr`, for instance, belong to the build plate adhesion settings.
+
+If the `limit_to_extruder` property evaluates to a positive number, instead of getting the setting from the object's extruder it will be obtained from the extruder written in the `limit_to_extruder` property. So even if an object is set to be printed with extruder 0, if the infill extruder is set to extruder 1 any infill setting will be obtained from extruder 1. If `limit_to_extruder` is negative (in particular -1, which is the default), then the setting will be obtained from the object's own extruder.
 
-If the `limit_to_extruder` property evaluates to a positive number, instead of getting the setting from the object's extruder it will be obtained from the extruder written in the `limit_to_extruder` property. So even if an object is set to be printed with extruder 0, if the infill extruder is set to extruder 1 any infill setting will be obtained from extruder 1. If `limit_to_extruder` is negative (in particular -1, which is the default), then the setting will be obtained from the object's own extruder.
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+This property is communicated to CuraEngine separately. CuraEngine makes sure that the setting is evaluated from the correct extruder. Refer to the [CuraEngine](#CuraEngine) chapter to see how this works.
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