/usr/share/vim/vimfiles/syntax
Edit: /usr/share/vim/vimfiles/syntax/modulefile.vim (2843B)
" include tcl syntax
set syntax=tcl
"Clear tcl keywords to match to avoid priority of keyword
" (e.g append vs append-path)
syn clear tclCommand
" set again tclCommand with `syn match`
" Basic Tcl commands: http://www.tcl-lang.org/man/tcl8.6/TclCmd/contents.htm
syn match tclCommand "\v<(after|append|array|bgerror|binary|cd|chan|clock|close|concat)>"
syn match tclCommand "\v<(dde|dict|encoding|eof|error|eval|exec|exit|expr|fblocked)>"
syn match tclCommand "\v<(fconfigure|fcopy|file|fileevent|flush|format|gets|glob)>"
syn match tclCommand "\v<(global|history|http|incr|info|interp|join|lappend|lassign)>"
syn match tclCommand "\v<(lindex|linsert|list|llength|lmap|load|lrange|lrepeat)>"
syn match tclCommand "\v<(lreplace|lreverse|lsearch|lset|lsort|memory|my|namespace)>"
syn match tclCommand "\v<(next|nextto|open|package|pid|puts|pwd|read|refchan|regexp)>"
syn match tclCommand "\v<(registry|regsub|rename|scan|seek|self|set|socket|source)>"
syn match tclCommand "\v<(split|string|subst|tell|time|trace|unknown|unload|unset)>"
syn match tclCommand "\v<(update|uplevel|upvar|variable|vwait)>"
" The 'Tcl Standard Library' commands: http://www.tcl-lang.org/man/tcl8.6/TclCmd/library.htm
syn match tclCommand "\v<(auto_execok|auto_import|auto_load|auto_mkindex|auto_reset)>"
syn match tclCommand "\v<(auto_qualify|tcl_findLibrary|parray|tcl_endOfWord)>"
syn match tclCommand "\v<(tcl_startOfNextWord|tcl_startOfPreviousWord)>"
syn match tclCommand "\v<(tcl_wordBreakAfter|tcl_wordBreakBefore)>"
" Modulefile commands: https://modules.readthedocs.io/en/stable/modulefile.html
syn match modCommand "\v<(append|prepend|remove)-path>"
syn match modCommand "\v<(prereq|prereq-all|prereq-any)>"
syn match modCommand "\v<(module|conflict|chdir|prereq)>"
syn match modCommand "\v
"
syn match modCommand "\v<(un)?set-(alias|function)>"
syn match modCommand "\v<(un)?setenv>"
syn match modCommand "\v<(un)?complete>"
syn match modCommand "\v"
syn match modCommand "\v"
syn match modCommand "\v"
syn match modCommand "\v"
syn match modCommand "\v"
syn match modCommand "\v"
syn match modCommand "\v"
syn match modCommand "\v<(system|uname|x-resource)>"
syn match modCommand "\v"
syn match modCommand "\v"
hi def link modCommand tclSpecial
syn match modProc "\v"
syn match modProc "\v"
syn match modProc "\v"
hi def link modProc tclSpecial
syn match modVar "\v"
syn match modVar "\v"
syn match modVar "\v"
syn match modVar "\v"
syn match modVar "\v"
hi def link modVar tclSpecial