Guidelines for range related properties (replaced by #1279)

[spectranaut]

This PR is to get feedback on range related property section to add to the APG.

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[css-meeting-bot]

The ARIA Authoring Practices (APG) Task Force just discussed Range related properties guidance.

The full IRC log of that discussion

<AnnAbbott> TOPIC: Range related properties guidance
<zcorpan> GitHub: https://github.com//pull/1000
<AnnAbbott> I'm back
<MarkMcCarthy> ey: above is a link to range related properties
<Jemma> https://github.com/w3c/aria-practices/blob/4207f97ceb0929ca8d9246d782f332c1b1573ef1/range_related_properties.md
<MarkMcCarthy> s/ey: above/ey: below
<AnnAbbott> mck: wants feedback on structure, missing info, where are others going to have questions
<AnnAbbott> jg: min/max not required on slider any longer
<Jemma> https://www.w3.org/TR/wai-aria-practices/examples/slider/slider-2.html
<Jemma> Slider Examples with aria-orientation and aria-valuetext
<AnnAbbott> jg: when has text value, numeric value doesn't make sense
<AnnAbbott> Simon: example doesn't use min/max
<zcorpan> s/doesn't/does/
<AnnAbbott> mck: high/med/low corresponds to 1, 2 and 3
<AnnAbbott> jg: there are good use cases for not having min/max
<AnnAbbott> jg: if something has text value, is it correct to use slider?
<AnnAbbott> Simon: where is an example without min/max?
<AnnAbbott> mck: what is purpose of min/max?
<AnnAbbott> jn: ARIA spec will not require min/max
<zcorpan> you can override the percentage rendering with aria-valuetext
<AnnAbbott> jn: if not specified, min = zero/max = 100
<AnnAbbott> mck: more work needed on this

[zcorpan]

I have converted this to HTML and rebased on master, but no new changes since @spectranaut had already addressed review feedback.

If this now looks OK, I think it should be ready for merge.

Here's a link to the preview of the new section.

[zcorpan]

@jongund can you review this? Thanks!

[zcorpan]

Replacing this PR with #1279