zcorpan: Given the following WPT test case:

<img title="title" data-expectedlabel="title" alt="" data-testname="img with tooltip label with empty alt" class="ex" src="data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==">

…and given the spec requirements at https://w3c.github.io/html-aam/#img-element-accessible-name-computation — specifically this requirement:

Otherwise use alt attribute, even if its value is the empty string.

…then it seems that the expectation for that test should be the empty string.
But as you can see, instead the expectation is title (from the title attribute value).
And https://wpt.fyi/results/accname/name/comp_tooltip.html shows that all engines pass that test.
So it seems like they’re all violating that “use alt attribute, even if its value is the empty string” spec requirement.

zcorpan: Ah wait I see: https://w3c.github.io/accname/#step2E says:

E. Host Language Label: Otherwise, if the current node's native markup provides an attribute (e.g. alt) or element (e.g. HTML label or SVG title) that defines a text alternative, return that alternative in the form of a flat string as defined by the host language, unless the element is marked as presentational (role="presentation" or role="none").

…<img alt=""> is role="presentation"