Newlines between HTML element attributes?

This is valid. as far as you don't break the attributes themselves. For example:

These are valid:

<a
href="http://example.com"
>
foobar

<a
href=
"http://example.com"
>
foobar</a>

This is not:

<a href="http://exampl
e.com">foobar</a>

Any white space is allowed between attribute definitions including spaces, tabs and newlines.

(Thanks Matt) Beware that:

<b>Some text</b>

is not equivalent to:

<b>
Some text
</b>

It is however equivalent to:

<b> Some text </b>

meaning those newlines are spaces.

Within an a tag definition between attributes however they are fine.