Clarification on button-layout 'behave as' definition and getComputedStyle().display discrepancy

[lpas]

What is the issue with the HTML Standard?

In the Button Layout Spec text found at https://html.spec.whatwg.org/multipage/rendering.html#button-layout, there is an ambiguity regarding the interpretation of the phrase "behave as 'inline-block'":

Otherwise, if the computed value of 'display' is a value such that the outer display type is 'inline', then behave as 'inline-block'.

The core question is: Does "behave as 'inline-block'" mean:

• The element's computed value for display should change to 'inline-block', and its box model behaves accordingly? (As seen in Chrome/WebKit)

• The element's computed value for display remains 'inline', but its box model is generated as if it were 'inline-block'? (As seen in Firefox)

Test Case Demonstrating Conflict

The current browser behavior is split:

let btn = document.createElement("button");
btn.style.display = "inline";
document.body.appendChild(btn);
console.log(getComputedStyle(btn).display);

Chrome/WebKit: inline-block
Firefox: inline