How do I allow only whole/fractional numbers in an input box

Here's the issue:

I'm trying to have a user be able to enter either a whole number or a fractional number (ie: 4.5) into a text input box on a mobile app. I would like to have the number pad show up so they can enter their input, but I'd rather not let them use the up/down arrows that go with the number input box, since they cannot go in .5 increments.

Can anyone shed any light on my options. I know I can use sprites to have users change their input up and down, but I'm looking for a simple, standard way of allowing users to enter numbers. I currently have input checked and made into a float, but when they use up and down arrows, it only steps up/down with whole numbers.

I hope I made sense. Any help would be greatly appreciated! :-) Thanks!

Anyone? C'mon, something as simple as this should be built into this already, but it isn't. How did you tackle this problem?

Set Attribute of your text input:

Attribute: "step"

Value: "0.5"

Awesome! Thank you! How did you know this about this? Is this written about somewhere?

Yes, I searched on Google and found here:

stackoverflow.com/questions/22228321/validate-0-5-as-step-value-in-html5-number-input