Question

I know that < is not used inside an HTML tag. I know that it is illegal in URIs too. I can deduce that it is also invalid in class or id of an HTML element. I have never seen it used in styles either.

I need to know however if there is any weird special case that < could be entered.

Let me elaborate. I want to match HTML tags in some text and say, throw them away. In this text, < is normally escaped (so written like \<), but I am assuming there could be user input mistake. So, I want to see if I there is ever a chance that such a thing could be a tag:

<.........<......>  <-- the whole thing is a tag

(where the .s could be anything, such as ")

Or could I safely assume the first < was a mistake by the user?

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The question sounds a bit too specific, so I’m going to make it a bit more general: What are the characters that absolutely cannot appear inside an html tag?

Answer 1

<a title="A title with a < less than symbol">My awesome link</a>

Is perfectly valid HTML.