Monday, December 3, 2012

ISimpleDOM support

As you probably know Firefox implements ISimpleDOM interfaces to provide a MS COM access to DOM in the browser. IE maintains similar interfaces. In accessibility world they were used to workaround lacks of MSAA API. Early days screen readers didn't have a choice how to make the browser accessible and they were DOM based.

Years later after IAccessible2 and UIA appeared the ISimpleDOM interfaces got obsolete. A bright demo of this statement is the NVDA screen reader which doesn't rely on ISimpleDOM at all and works nicely with Firefox. Nonetheless periodically I hear that ISimpleDOM is still very useful for AT. As a rule this opinion comes from proprietary screen reader vendors so I don't really aware of details. We trust them and we continue to support ISimpleDOM. However we don't recommend anyone to use ISimpleDOM.

We consider ISimpleDOM as optional API and thus we think that our support of it shouldn't affect on AT software that don't rely on ISimpleDOM. As a first part of this idea the ISimpleDOMNode interface was implemented as a tear off. That means whenever you query ISimpleDOMNode interface you always get a new instance implementing this interface. That allows us to save 4 bytes per accessible object and that was good for memory usage. The change was landed on Firefox 20.

We didn't find any problems during testing stage but if you would like to give it a spin, please try a nightly build. Especially it makes sense if you are developer of AT software relying on ISimpleDOM. Please let us know if you have concerns.

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