I think that is the key point. A conventional label is simple and doesn't need all this extra support to be helpful to the user. I've never really liked the "label in the field" trend except in really simple forms where there's almost no chance for ambiguity anyway.
I never really thought why they were called 'placeholder' before but it makes sense; they are not labels, they are examples.
Everything else (like putting the labels to the left of the field or in the field) and you start seeing errors increase in form submissions. So it is to be avoided.
Part of that was simplifying the look of the checkout, which includes putting the labels inside of the inputs.
Not to mention some very notable websites use this design choice, including Square, Twitter, and Apple.
Because they seems to think that the placeholder as label works well [0].
* Don't make your label use the same style as user-entered text.
I remember encountering a website that failed to do this, while satisfying all the other points. It was super confusing to learn that the texts were just labels and not pre-filled values, since they had the exact same color as the text I entered (unlike HTML5 placeholders that are dimmed).Plus it will hurt your SEO. All the search engine sees is some form fields and little else.
There is no try.
If you cannot move it to a reasonable location, do not use this method.
Also, on other note: username is Not an email address. Do not ask me for my username when you really mean email address.
Oh, and one more thing. Let me know (or make it easy to find out) what special rules you require for passwords on your login page. Your site is annoying because you probably require some special combinate of letters and numbers and possibly something else, which means I have to figure out which password pattern I should be trying.
Are you saying that sites should allow users to use email addresses to log in, rather than usernames? As I understand it, the former is a more recent thing.
I can't stand it when I try and log in to a website and fail 4 times. Then finally click "Forgot Username" and all that pops up is a box saying my username is my email address.