Animate auto height

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  "title": "Animate auto height",
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    "scene": "One native button followed by a clipped wrapper containing independently written, noninteractive explanatory text. Put padding on an inner element so height zero does not retain outer padding.",
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        "label": "Expand / Collapse",
        "type": "button",
        "action": "In animated mode toggle desiredOpen, update aria-expanded, and animate toward auto or zero. In static/reduced-motion mode disable this button, keep desiredOpen and aria-expanded true, and label the visible state Expanded."
      },
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        "label": "Short / Long text",
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      },
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        "type": "toggle",
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    "durationSeconds": 0.4,
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    "initialAnimatedState": "collapsed",
    "shortTextLength": "one new sentence",
    "longTextLength": "three new paragraphs",
    "assets": "system font and original text only"
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  "verificationRequired": [
    "At open completion the wrapper has natural height and all text is visible; at closed completion its content box height is zero.",
    "Rapid expand-collapse-expand ends in the last requested state without an old completion callback changing the height.",
    "Switch long text and resize from 1440px to 320px while opening; no lasting clipped text remains after settling.",
    "Keyboard activation updates aria-expanded. Static, reduced-motion, and no-JavaScript states expose text with aria-expanded=true and the collapse button disabled; returning to animated mode keeps content open until the next action."
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  "unsupportedClaims": [
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    "An auto endpoint is measured for a tween; this is not a guarantee of continuously tracking content changes during that tween."
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