[gui]
    tabsize = 4

catch {$ui_diff configure -tabstyle wordprocessor}

catch {$ui_diff configure -tabs "[expr {4 * [font measure $font 0]}]" -tabstyle wordprocessor}

catch {$ui_diff configure -tabstyle wordprocessor}`

catch {$ui_diff configure -tabs "[expr {[get_config gui.tabsize] * [font measure font_diff 0]}] left" -tabstyle wordprocessor}