Actually, in some cases, the web browser will display a document exactly the way it receives it from the web server. For example, if the document requested is an image, the web browser will display it directly. Similarly, plain text files will be displayed just as they are sent. Actually, though HTML is often called a programming language it is really not.
Programming languages are 'Turing-complete', or 'computable'.
That is, programming languages can be used to compute something such as the square root of pi or some other such task. Typically programming languages use conditional branches and loops and operate on data contained in abstract data structures. HTML is much easier than all of that. HTML is simply a 'markup language' used to define a logical structure rather than compute anything. It is sort've a semantic issue, but it is one which you should officially be aware of.