Does bash (or zsh) "officially" mandate the use of tabs for indentation in scripts?

I recently came across the following statement (source ; emphasis added): > For shell scripts, using tabs is not a matter of preference or style; *it's how the language is defined*. I am trying to make sense of this claim. Of course, it is somewhat loosely worded1, but I would like to know if there is any truth to it. In particular, I would like to know if the official documentation for either bash or zsh (the two shells I routinely write scripts for) say anything approaching a mandate or recommendation to use tabs for indentation of source code. (I would appreciate explicit references to the supporting paragraphs in this documentation.) (FWIW, let me point out that I am aware of the fact that, in practice, both bash and zsh readily interpret scripts that are *not* indented exclusively with tabs. Therefore, I don't expect the documentation for either shell to go much further than a strong recommendation, if they mention the matter at all.) --- 1 For one thing, it refers simultaneously to "shell scripts" and "the language", which contradicts the facts that there are multiple shells in current use, each defining its own language.