Newlines and special characters in HTML attributes

Question

My questions are simple:

Is the following valid? If it is, would it break in some browsers?

<div data-text="Blah blah blah
More blah
And just a little extra blah to finish"> ... </div>

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Which characters "must" be encoded in attribute values? I know " should be ", but are any others required to be encoded?

Answer 1

Is the following valid?

It's a valid fragment of HTML5, yes.

would it break in some browsers?

Unlikely.

Which characters "must" be encoded in attribute values? I know " should be ", but are any others required to be encoded?

That depends on whether the attribute value is double quoted, single quoted or unquoted.

For the double quoted form " must be replaced by its character reference, and & may need to be replaced by its character reference depending on the characters that follow it. See attribute-value-double-quoted-state

For the single quoted form ' must be replaced by its character reference, and & may need to be replaced by its character reference depending on the characters that follow it. See attribute-value-single-quoted-state

For the unquoted form TAB, LINEFEED, FORMFEED, SPACE, > must be replaced by their character references, and & may need to be replaced by its character reference depending on the characters that follow it. See attribute-value-unquoted-state

Answer 2

HTML 5 spec

There are different requirements for different attributes so there isn't one answer. For instance, title attributes allow lines feeds, but a class attribute is a space seperated line of string tokens.

For data elements though the spec says of the namespace:

contains no characters in the range U+0041 to U+005A (LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).

Other than that, it doesn't make any distinctions.