The underlying Windows control (UPDOWN_CLASSW) that uiSpinbox uses is integer only, doesn't support floating point values.

Unix and Darwin controls do support this though, and we enforce integer only just for compatibility with Windows.

Ah okay. Seems like this would be a good thing to put in the spinbox documentation in case people are looking for one that does floats. Is there a way to implement a custom widget that does this? For now I'll fall back to using a uiEntry and parse the values in my own code.

Is there a way to implement a custom widget that does this?

It does seem like a custom control would be possible using the win32 API by overriding some of the handlers as suggested here and here.

So it does look like writing a uiSpinboxDouble would be possible, Windows being the only cumbersome undertaking.