Also, older HTML allowed you to not quote the information after the equal sign in some circumstances.

Newer HTML too; it is only XHTML that makes quoting attribute values mandatory in all circumstances.

Since email addresses will include an @ character, the attributes are mandatory in this case.

That said, it isn't as if nobody ever breaks the rules, so it is generally a good idea to write code that can cope (unless you know that the incoming data won't have that problem).

In reply to Quoting attribute values in HTML by dorward
in thread How to extract an email address from a mailto URL? by jdlev

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