The open property of the HTMLDetailsElement interface is a boolean value reflecting the open HTML attribute, indicating whether the <details>'s contents (not counting the <summary>) is to be shown to the user. 
 The open property of the HTMLDetailsElement interface is a boolean value reflecting the open HTML attribute, indicating whether the <details>'s contents (not counting the <summary>) is to be shown to the user. 
A boolean value.
The boolean value represents the state of the open HTML attribute. The value of true means it is set with both the summary and the additional information shown to the user. The false value means it not set, with only the summary shown.
| Specification | 
|---|
| HTML Standard  # dom-details-open  | 
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
open | 
10 | 79 | 49 | No | 15 | 6 | ≤37 | 18 | 49 | 14 | 6 | 1.0 | 
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    https://developer.mozilla.org/en-US/docs/Web/API/HTMLDetailsElement/open