Eskil

    addPrefMultOpt -excludedir dir,exdirs
    docFlag    -excludedir "Exclude from directory diff"
    addPrefMultOpt -excludefile dir,exfiles
    docFlag    -excludefile "Exclude from directory diff"
    # These affect Pref but via special processing later
    addMultOpt -prefix
    docFlag    -prefix "Care mainly about words starting with <str>"
    addMultOpt -subst
    docFlag    -subst  "The <pair> is a list of Left+Right, used for subst preprocessing"
    addMultOpt -preprocess
    addMultOpt -preprocessleft
    addMultOpt -preprocessright
    docFlag    -preprocess  "The <pair> is a list of RE+Subst applied to each line before compare"
    docFlag    -preprocessleft  "Use <pair> only on left side"
    docFlag    -preprocessright "Use <pair> only on right side"
    # These affect opts

        foreach apa $arg {
            set RE [string map [list % $apa] {^.*?\m(%\w+).*$}]
            if {$::Pref(nocase)} {
                set RE "(?i)$RE"
            }
            addPreprocess prefix $RE {\1} ""
        }
    }
    if {[optIsGiven -subst arg]} {
        # FIXA: better validity check
        foreach apa $arg {
            foreach {left right} $apa {
                if {$::Pref(nocase)} {
                    set left "(?i)$left"
                    set right "(?i)$right"
                }
                addPreprocess subst $left $right Subst
            }
        }
    }
    if {[optIsGiven -preprocess arg]} {
        # FIXA: better validity check
        foreach apa $arg {
            foreach {RE sub} $apa {
                addPreprocess cmdline $RE $sub ""
            }