Nonstandard HTML tags?

Question

HTML

Good evening.
I want to clarify one question.
What are the effects of non-standard html tags.
Examples I want to use

//1
<div class="default-class"></div>
<default-class></default-class>


//2
<span class="border-color"></div>
<border-color></border-color>

Is there a difference between them, search engines and other services will respond to them normally?

Answer 1

Search engines will see this tag without problems, because HTML is just a subset of SGML. But such tags will not carry any semantic load. In short, the search robot will see them as <div>