I agree with all of this, though the comment about not being able to execute it, but rather being used as input for a program, had me thinking twice. I want to play devil’s advocate just for a second.

Code written using interpreted languages like Python and Ruby would fall into being “input for a program”.

You can even say that Unrealscript can’t execute, as it’s data for a program (game) that uses the Unreal engine. Or C# for a Untiy game.

Compiled C# IL code doesn’t even execute without the .Net runtime. Same for Java bytecode without the Java VM.

I would say it’s not a stretch to consider all of the above as “programming languages” because they have a couple of things in common: mutability/manipulation of variables and control structures. End devil’s advocate.

HTML allows you to define variables that live in the DOM, but you cannot do much to really manipulate them without Javascript. The user can manipulate them through the browser via input controls which are defined in HTML, but that’s the extent of HTML’s involvement of it, AFAIK.

HTML doesn’t have a way of defining control structures like you’d expect from a programming language. You can really stretch and say that a table is a double for loop, albeit consisting only of display instructions. There may be conditionals, to display data differently based on attributes, especially with the help of CSS. However this is, in multiple orders of magnitude, less capable of complexity than what every “programming language” has in common.

Circling back to Scotty’s point, he’d be correct in saying that HTML is data, which is unlike the way that the other aforementioned languages are.