Can String + Format still pass when not exact match?

**Describe the bug**
As per the Codepen example, like `moment` can `dayjs` still return a date even if only a partial match is found? I understand an array of format options can also be supplied. But am wondering if the specificity required is intentional? Or is it a bug?
https://codepen.io/MichaelHeyDonny/pen/rNzNPRJ

**Expected behavior**
Still return a dayjs object with what can be retrieved.