Thread:Project:Support desk/Template to show HTML as plain text/reply (7)

Its not all that commonly used, I'm not sure if it has a name - but its documented on help:Magic Words (near the bottom). But basically any &lt;tag-name&gt; type extension, can also be called using syntax. The difference is, that in the  version, no wikitext is expanded (by default anyways, the extension itself can expand wikitext if it wants, for example  does, although pre-save-transform is never done), but when it is called as 's, templates, and parser funcs are expanded, and pre-save-transform (converting ~ to signature's, pipe-trick, and subst:) is done.