Clarify usage vs data index semantics in HID report parsing

Adds clarification that HID usages do not uniquely identify value instances and do not define report order. Recommends using data indices (HidP_GetData) for complete and unambiguous value retrieval.

Author: DJm00n

windows-driver-docs-pr/hid/interpreting-hid-reports.md

@@ -63,16 +63,18 @@ An application or driver can set the state of buttons in a properly initialized
 
 ## Extracting and setting control data by data indices
 
+[HidP_GetUsageValue](/windows-hardware/drivers/ddi/hidpi/nf-hidpi-hidp_getusagevalue) assumes that a [usage](./hid-usages.md) uniquely identifies a value instance. This is not guaranteed by the HID specification. A usage defines the meaning of a control, but not a unique value instance within a report. Multiple values in a report may share the same usage, and their order is defined by the report layout, not by usage values. Data indices uniquely identify each value and preserve report order. HidP_GetData should be used when complete and unambiguous input data is required.
+
 To use data indices to extract and set control data in a HID report, an application or driver can use the following [HIDClass support routines](/windows-hardware/drivers/ddi/_hid/#hidclass-support-routines):
 
 - [HidP_GetData](/windows-hardware/drivers/ddi/hidpi/nf-hidpi-hidp_getdata)
 - [HidP_SetData](/windows-hardware/drivers/ddi/hidpi/nf-hidpi-hidp_setdata)
 
 These routines are useful to an application or driver that provides a "value-added" service. For example, one that provides a custom interface to all the controls supported by a HIDClass device. Microsoft DirectInput is one example.
 
-An application or driver calling these routines can most efficiently obtain and set all values in a report. For example, to obtain all value data by their [HID usages](./hid-usages.md), it has to call [HidP_GetUsageValue](/windows-hardware/drivers/ddi/hidpi/nf-hidpi-hidp_getusagevalue) for each usage. However, to obtain all value data by data index, it only has to call **HidP_GetData** once.
+An application or driver calling these routines can most efficiently obtain and set all values in a report. For example, retrieving values by [usage](./hid-usages.md) requires calling [HidP_GetUsageValue](/windows-hardware/drivers/ddi/hidpi/nf-hidpi-hidp_getusagevalue) for each usage, while [HidP_GetData](/windows-hardware/drivers/ddi/hidpi/nf-hidpi-hidp_getdata) retrieves all values in a single call using data indices.
 
-An application or driver uses the data indices specified in a collection's [Button Capability Arrays](./button-capability-arrays.md) and [Value Capability Arrays](./value-capability-arrays.md) to identify HID usages.
+An application or driver uses the data indices specified in a collection's [Button Capability Arrays](./button-capability-arrays.md) and [Value Capability Arrays](./value-capability-arrays.md) to associate data indices with HID usages.
 
 ## See also