Describe requester passing reserved parameter value (#1168)

* Improve default vs. fixed language

Co-authored-by: Emanuel Tesař <[email protected]>

docs/airnode/v0.10/grp-providers/guides/build-an-airnode/api-integration.md

@@ -346,7 +346,7 @@ specify a large number of endpoint parameters at no additional gas cost.
 Note that there are some cases where you may not want to map endpoints to API
 operations one-to-one. For example, an API operation can have a `header`
 parameter, `Accept`, that can take the values `application/json` or
-`applicatino/xml` to determine how to format the data that the API will respond
+`application/xml` to determine how to format the data that the API will respond
 to the call. Airnode expects responses to be in JSON format, and thus
 hard-coding this parameter as `JSON` would be more suitable than letting the
 requester decide, as there is only one valid choice. Again, the integrator's job

docs/ois/v1.0/ois.md

@@ -464,13 +464,12 @@ Allowed values: `_type`, `_path` or `_times`
 #### 5.4.2. `fixed`
 
 (Optional) The fixed (i.e., non-overridable) value for the reserved parameter.
-If `fixed` is used, `default` has no effect and should not be used.
+Cannot be used together with `default`.
 
 #### 5.4.3. `default`
 
 (Optional) The default value for the reserved parameter. Used when no value is
-provided. If `default` is used, `fixed` must not be used because it would
-override the default value.
+provided. Cannot be used together with `fixed`.
 
 ### 5.5. `parameters`
 

docs/ois/v1.1/ois.md

@@ -465,13 +465,12 @@ Allowed values: `_type`, `_path` or `_times`
 #### 5.4.2. `fixed`
 
 (Optional) The fixed (i.e., non-overridable) value for the reserved parameter.
-If `fixed` is used, `default` has no effect and should not be used.
+Cannot be used together with `default`.
 
 #### 5.4.3. `default`
 
 (Optional) The default value for the reserved parameter. Used when no value is
-provided. If `default` is used, `fixed` must not be used because it would
-override the default value.
+provided. Cannot be used together with `fixed`.
 
 ### 5.5. `parameters`
 

docs/ois/v1.2/ois.md

@@ -465,13 +465,12 @@ Allowed values: `_type`, `_path` or `_times`
 #### 5.4.2. `fixed`
 
 (Optional) The fixed (i.e., non-overridable) value for the reserved parameter.
-If `fixed` is used, `default` has no effect and should not be used.
+Cannot be used together with `default`.
 
 #### 5.4.3. `default`
 
 (Optional) The default value for the reserved parameter. Used when no value is
-provided. If `default` is used, `fixed` must not be used because it would
-override the default value.
+provided. Cannot be used together with `fixed`.
 
 ### 5.5. `parameters`
 

docs/ois/v1.3/ois.md

@@ -465,13 +465,12 @@ Allowed values: `_type`, `_path` or `_times`
 #### 5.4.2. `fixed`
 
 (Optional) The fixed (i.e., non-overridable) value for the reserved parameter.
-If `fixed` is used, `default` has no effect and should not be used.
+Cannot be used together with `default`.
 
 #### 5.4.3. `default`
 
 (Optional) The default value for the reserved parameter. Used when no value is
-provided. If `default` is used, `fixed` must not be used because it would
-override the default value.
+provided. Cannot be used together with `fixed`.
 
 ### 5.5. `parameters`
 

docs/ois/v1.4/ois.md

@@ -459,6 +459,12 @@ Each object has the following elements:
 - `fixed`
 - `default`
 
+Note that if a reserved parameter object does not include a `fixed` value, a
+requester can, or may be expected to, supply this value as a parameter. A value
+supplied by a requester overrides a `default`. See the
+[\_gasPrice reserved parameter description](./reserved-parameters.md#gasprice)
+for an example.
+
 #### 5.4.1. `name`
 
 (Required) The name of the reserved parameter. Always starts with `_`.
@@ -468,13 +474,12 @@ Allowed values: `_type`, `_path`, `_times`, and `_gasPrice`.
 #### 5.4.2. `fixed`
 
 (Optional) The fixed (i.e., non-overridable) value for the reserved parameter.
-If `fixed` is used, `default` has no effect and should not be used.
+Cannot be used together with `default`.
 
 #### 5.4.3. `default`
 
 (Optional) The default value for the reserved parameter. Used when no value is
-provided. If `default` is used, `fixed` must not be used because it would
-override the default value.
+provided by a requester. Cannot be used together with `fixed`.
 
 ### 5.5. `parameters`
 

docs/ois/v1.4/reserved-parameters.md

@@ -28,8 +28,10 @@ There are two types of parameters which are part of the OIS object:
 1. [Endpoint parameters](./ois.md#_5-5-parameters) - Airnode endpoint parameters
    are mapped to API operation parameters.
 2. [Reserved parameters](./ois.md#_5-4-reservedparameters) - Reserved parameters
-   perform a specific operation on the response before fulfilling the request.
-   Reserved parameter names start with `_`.
+   perform a specific operation related to the request or on the response before
+   fulfilling the request. Reserved parameter names start with `_`. Depending on
+   the configuration, they may be overridden by a parameter supplied by a
+   requester.
 
 ## `_type`