Is it acceptable to use single quotes around values in HTML attributes? [duplicate]

Question

Is it acceptable to use single quotes around html attribute values like this:

<span class='classname'>Hi</span>

Instead of double quotes like this:

<span class="classname">Hi</span>

Who defines what's okay? W3C?

Answer 1

Yes, that's acceptable. It works in browsers, and it's allowed by the specifications.

The HTML5 spec says:

In the HTML syntax, attributes can be specified in four different ways:

1. empty attribute syntax
2. unquoted attribute-value syntax
3. single-quoted attribute-value syntax
4. double-quoted attribute-value syntax

The HTML4 spec says:

By default, SGML requires that all attribute values be delimited using either double quotation marks (ASCII decimal 34) or single quotation marks (ASCII decimal 39). Single quote marks can be included within the attribute value when the value is delimited by double quote marks, and vice versa.