Is It Guaranteed That Non-numeric Attribute Values On Every Web-page HTML Are Always Quoted?

I'm parsing the source code of different web pages. I'm not sure whether or not it is guaranteed that it will always be in HTML format, but for the sake of this question, it is all

Solution 1:

The HTML standard doesn't require attributes to be quoted, see HTML5 - The HTML syntax - Attributes

8.1.2.3 Attributes
...
Attributes can be specified in four different ways:
Empty attribute syntax
Unquoted attribute value syntax
Single-quoted attribute value syntax
Double-quoted attribute value syntax