Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
Summary
Element.runtimeStyle is a proprietary property similar to HTMLElement.style, except its styles, that have higher precedence and modification. It does not modify the style content attribute. It is available in old versions of Microsoft Internet Explorer.
Specification
Not a part of any specification.
Microsoft has a description on MSDN.
Browser compatibility
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Microsoft Edge | Opera | Safari (WebKit) |
|---|---|---|---|---|---|---|
| Basic support | No support | No support | 6 | No support | No support | No support |
| Feature | Android | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | No support | No support | ? | ? | No support |