We recommends quotes in HTML, and demands quotes for stricter document types like XHTML.
Using quotes are the most common. Omitting quotes can produce errors. We always use quotes around attribute values.
Double quotes around attribute values are the most common in HTML, but single quotes can also be used.
In some situations, when the attribute value itself contains double quotes, it is necessary to use single quotes. Or vice versa.
<p title='John "ShotGun" Nelson'>.
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