It appears that the Kate editor has a lot of xml files describing various languages, for highlighting purposes. For example, commonlisp.xml contains all 978 standard Common Lisp symbols. Other projects depends on these files, like Skylighting in Haskell and then indirectly matterhorn.
But commonlisp.xml also define a mysterious TRUNCASE function at line 901, which does not exist in the standard.
The vim editor also define this function, in runtime/syntax/lisp.vim.
I suspect the vim file to be generated from the Kate one, or inversely, or from the same source as Kate.
The above file also says:
Clisp additions courtesy of http://clisp.cvs.sourceforge.net/*checkout*/clisp/clisp/emacs/lisp.vim
We can find the file on sourceforge, but there is no mention of truncase here:
https://sourceforge.net/p/clisp/clisp/ci/default/tree/emacs/lisp.vim
But maybe there is another Lisp implementation that used to define this function.
So I'm wondering if this is all just a bug that survived the passage of time and made its way into various projects, or if there is a good reason for this function to be added to the list of Lisp symbols.
Was there ever a TRUNCASE function defined as part of a Lisp dialect?
There is no mention of this symbol anywhere else and it is unlikely that it ever existed. The linked code is probably a bug and a fix was submitted and merged.