Microsoft's new Persian Standard Keyboard in Windows 10 seems to be an implementation of ISIRI-9147. In light of this, I came across an issue where I needed to type in the Arabic Subscript Alef (U+0656). As per the standard, the character is supported as a third-level mapping of "V" on Latin keyboards. On my macOS system, I do this by typing Option-v.
The third-level modifier key defined in the standard is Alt or Alt-Gr (depending on the hardware keyboard layout being either ANSI or ISO). I know this is going to be problematic on Windows because Alt combinations are normally reserved for menu shortcuts. I wonder if and how Microsoft has implemented this part of the standard. As an example, I would like to reproduce this string on Windows: ابیٖ