aom-example.js

// default role is "slider"
// set using private accessibleNode by the element author
<custom-slider id="mySlider">

// element consumer changes role to "button"
mySlider.accessibleNode.role = "button"

// element consumer nulls role
mySlider.accessibleNode.role = null

// element falls back to default role
getComputedAccessibility(mySlider.accessibleNode).role // 'slider'

// note: the ability to compute the accessibility tree is
// a phase 4 AOM proposal. The line above is pseudo code :)