In general computer
jargon one
codes in a
programming language. What is that ? At least to me, it is a
Turing-complete language, that is to say, one that has at least a
conditional jump instruction (and all the usual arithmetica stuff).
Does HTML have that ? No. The fine art of stuffing a text with tags is called to mark up.
So one codes PASCAL, C, AppleScript, sendmail.cf: and marks up in SGML, HTML and troff.
I had previously included TeX as a markup language: luckily WWWWolf reminded me that TeX is a real macro language, and you can write real programs with it...