What does illegal mean in the context of HTML?

To use it in a sentence (no pun intended), it's illegal to place a div inside an inline tag. – MrPersonHumanGuy (talk) 01:15, 2 September 2025 (UTC)

It violates the specs of the HTML syntax, is not correct HTML, and may be expected to cause renderers to behave erratically. Aaron Liu (talk) 03:05, 2 September 2025 (UTC)

The word "illegal" is being improperly used. It should be "invalid" as there are no laws or government regulations governing use of HTML for the general public. You cannot be arrested or summoned to a court of law for placing a div inside an inline tag, but you will end up with invalid syntax and all the cool kids will point at you and laugh. 68.187.174.155 (talk) 09:59, 8 September 2025 (UTC)

There's nothing improper about this use. It's just a different meaning of the same word. The Oxford English Dictionary gives three definitions of "illegal"; the first is "Not legal or lawful; against, contrary to, or forbidden by, law", which is the meaning you have in mind. The second is "Irregular, unorthodox, deprecated. Now esp.: not permitted or that cannot be performed by an electronic device, computer program, etc.", and the first quotation in this sense is from 1728. CodeTalker (talk) 03:00, 9 September 2025 (UTC)

You'll also find the word "illegal" used this way in a few other "rules" based systems such as Lego or Minecraft. ―Panamitsu (talk) 03:38, 9 September 2025 (UTC)