docs: RFC - Number Field Stepping

[AndrewLeedham]

RFC for a new prop interval for the NumberField component/hook which influences how incrementing/decrementing works outside of the step prop.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

RFC: N/A

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Onyx Insight

[snowystinger]

Thanks for the RFC, we had a discussion about this today and have some questions.

How do we want to define step and interval? I know you've highlighted this in the drawbacks section.

Currently, step is both clamping behaviour and the delta that the arrows move by, impacted by the minValue. This is how native number fields work. https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Attributes/step#min_impact_on_step

We have some options. We can either continue with the current definition closely when both are used:
step is clamping behaviour
interval is only how much the arrowup/down moves

Or we could flip the definitions:
step is only how much the arrowup/down moves
interval is clamping behaviour

We'll also probably want to make some errors during development for invalid combinations of the props. These are two we thought might be useful, are there others?

Some other interactions that may exist are the Number formatter options.

NumberField() {
let {
  step,
  interval = step
} = props

// don't forget to include minValue starting point
if (step % interval !== 0) throw?? round (based on format options?)?? totally fine??
if (step > interval) throw??

step will need to stay and will need to behave the same when the other prop isn't there so this is non-breaking. We haven't thought of a better name for interval yet, but perhaps that will come out after determining the definition we want.

An example of usage that might be confusing depending on how we defined these props.

step 10
interval 3
minValue 4
current value is 4
press arrow up -> 14

rounds to 13 (based on minValue impact, valid values are 4, 7, 10, 13, 16) (numberformat options rounding influences this??)
rounds to 15? (don't base on minValue impact when both props are specified? then valid values are 6, 9, 12, 15)