\documentclass[
ukenglish,%
twoside=false,%
fontsize=10pt,%
bibliography=totoc,%
numbers=autoenddot,%
headings=normalsize,%
overfullrule,%
headings=optiontotoc,%
]
{scrartcl}

\makeatletter
\providecommand\@ix{9.6}
\providecommand\@xi{10.4}
\providecommand\@xiii{13.15}
\def\subfootnotesize{%
    \@setfontsize%
    \subfootnotesize%
    {7.6}{8}%
}
\def\supernormalsize{%
    \@setfontsize%
    \supernormalsize%
    \@xi{12}%
}
\def\subnormalsize{%
    \@setfontsize%
    \subnormalsize%
    \@ix{11}%
}
\def\sublarge{%
    \@setfontsize%
    \sublarge%
    {11.2}{13}%
}
\def\superlarge{%
    \@setfontsize%
    \superlarge%
    \@xiii{16}%
}
\makeatother

\newcommand*{\sectionas}{2.3ex plus .2ex}
\newcommand*{\sectionbs}{-3.5ex plus -1ex minus -.2ex}
\newcommand*{\sectiontbs}{3.6pt}
\newcommand*{\subsectiontbs}{1.2pt}
\newcommand*{\subsectionas}{1.5ex plus .2ex}
\newcommand*{\subsectionbs}{-3.25ex plus -1ex minus -.2ex}
\newcommand*{\subsubsectionas}{\subsectionas}
\newcommand*{\subsubsectionbs}{\subsectionbs}
\newcommand*{\paragraphas}{-1em}
\newcommand*{\paragraphbs}{.8\baselineskip}

\newlength{\tnwsection}
\newlength{\tnwsubsection}
\newlength{\tnwsubsubsection}
\newlength{\tnwparagraph}
\newlength{\tisection}
\newlength{\tisubsection}
\newlength{\tisubsubsection}
\newlength{\tiparagraph}

\setlength{\tnwsection}{1.2em}
\addtolength{\tnwsection}{.6em}
\setlength{\tnwsubsection}{\tnwsection}
\addtolength{\tnwsubsection}{.75em}
\setlength{\tnwsubsubsection}{\tnwsubsection}
\addtolength{\tnwsubsubsection}{.75em}
\setlength{\tnwparagraph}{\tnwsubsubsection}
\addtolength{\tnwparagraph}{.75em}

\setlength{\tisection}{0em}
\setlength{\tisubsection}{\tisection}
\addtolength{\tisubsection}{\tnwsection}
\setlength{\tisubsubsection}{\tisubsection}
\addtolength{\tisubsubsection}{\tnwsubsection}
\setlength{\tiparagraph}{\tisubsubsection}
\addtolength{\tiparagraph}{\tnwsubsubsection}

\RedeclareSectionCommands[%
    tocraggedentrytext=true,%
]%
{section,subsection,subsubsection,paragraph}

\RedeclareSectionCommand[%
    tocindent=\tisection,%
    tocnumwidth=\tnwsection,%
    tocbeforeskip=\sectiontbs,%
    tocentryformat=\supernormalsize\sffamily\bfseries,%
    tocentrynumberformat=\supernormalsize\sffamily\bfseries,%
    tocpagenumberformat=\supernormalsize\sffamily\bfseries%
]%
{section}

\RedeclareSectionCommand[%
    tocindent=\tisubsection,%
    tocnumwidth=\tnwsubsection,%
    tocbeforeskip=\subsectiontbs,%
    tocentryformat=\subnormalsize,%
    tocentrynumberformat=\subnormalsize,%
    tocpagenumberformat=\subnormalsize%
]%
{subsection}

\RedeclareSectionCommand[%
    tocindent=\tisubsubsection,%
    tocnumwidth=\tnwsubsubsection,%
    tocbeforeskip=\sectiontbs%
]%
{subsubsection}

\RedeclareSectionCommand[%
    afterskip=\paragraphas,%
    beforeskip=\paragraphbs,%
    tocindent=\tiparagraph,%
    tocnumwidth=\tnwparagraph,%
    tocbeforeskip=\sectiontbs%
]%
{paragraph}

\linespread{1.1}

\newcommand*{\hs}{\hspace{.45em}}

\usepackage{fontspec}

\directlua{

    fonts.handlers.otf.addfeature {
        name = "onumkern",
        type = "kern",
        data = {
            ["v"] = { ["zero.taboldstyle"] = 80 },
            ["two.taboldstyle"] = { ["zero.taboldstyle"] = 30, ["/"] = 50 },
            ["five.taboldstyle"] = { ["/"] = 20 },
            ["»"] = { ["I"] = 50 },
        },
    }

}

\setmainfont{Tangent}[
    BoldFont = *-Medium,
    ItalicFont = *-Italic,
    Ligatures = {Common, TeX},
    Numbers = OldStyle,
    RawFeature = +onumkern
]

\setsansfont{SegoeUI}[
    BoldFont = seguisb.ttf,
    Ligatures = {Discretionary, TeX},
    Numbers = OldStyle
]

\setmonofont{Consolas}[
    ItalicFont = *-Italic,
    Numbers = OldStyle
]

\newcommand*{\mono}[1]{%
    {\subnormalsize\texttt{#1}}%
}

\usepackage{babel}
\usepackage[paper=a4paper,marginratio={2:1,3:4}]{geometry}
\usepackage{spacekern}
\usepackage{hyperref}
\usepackage{bookmark}
\usepackage{microtype}

\hypersetup{%
    pdflang=en,%
    unicode=true,%
	pdfborder={0 0 0},%
	bookmarksopen=true,%
    bookmarksopenlevel=0,%
	bookmarksnumbered=true,%
    pdftitle={The showkerning package},
    pdfsubject={Showing kerns in a document},
    pdfauthor={Thomas Kelkel},
    pdfkeywords={tex, latex, kerning}
}

\setlength{\parindent}{0pt}
\setlength{\parskip}{.4\baselineskip}

\newcommand*{\q}[1]{%
    ›%
    #1%
    ‹%
}
\newcommand*{\qq}[1]{%
    »%
    #1%
    «%
}

\newcommand*{\textnote}[1]{%
    {%
        \ttfamily%
        \char174{}%
        #1%
        \char174{}%
    }%
}

\usepackage{luacode}

\begin{luacode}

local FLOOR = math.floor

local function round ( num, dec )
    return FLOOR ( num * 10^dec + 0.5 ) / 10^dec
end

local p_array = {false, false, false, false, false}
local p_counter = 0
local ID = node.id
local NEW = node.new
local COPY = node.copy
local REM = node.remove
local PREV = node.prev
local NEXT = node.next
local TAIL = node.tail
local T_ID = node.traverse_id
local T_GLYPH = node.traverse_glyph
local INS_B = node.insert_before
local GLYPH = ID ( "glyph" )
local GLUE = ID ( "glue" )
local KERN = ID ( "kern" )
local HLIST = ID ( "hlist" )
local SWAPPED = table.swapped
local SUBTYPES = node.subtypes
local SPACESKIP = SWAPPED ( SUBTYPES ("glue") )["spaceskip"]
local WIDTH = round ( tex.sp ( "1.6em" ), 0 )
local ipairs = ipairs
local page_counter = 0
local INS_A = node.insert_after
local p_counter_x = 0
local ATC = luatexbase.add_to_callback

local function make_marks ( head, char, id, array, counter )
    for n in T_GLYPH ( head ) do
        if n.char == char then
            counter = counter + 1
            array[counter] = {false, false, false}
            head = INS_B ( head, n, NEW ( GLYPH ) )
            PREV ( n ).data = id
            local NEXT = n.next
            local inside_counter = 0
            while NEXT.char ~= char do
                inside_counter = inside_counter + 1
                array[counter][inside_counter] = COPY ( NEXT )
                NEXT = NEXT.next
                REM ( head, NEXT.prev )
            end
            head = REM ( head, NEXT )
            head = REM ( head, n )
        end
    end
    return head, array, counter
end

local function mark_notes ( head )
    head, p_array, p_counter = make_marks ( head, 174, 427956, p_array, p_counter )
    return head
end

local function make_margin_notes ( head, id, array, counter )
    for n in T_ID ( HLIST, head ) do
        local first_kern = 0
        local first_width = 0
        for glyph_node in T_GLYPH ( n.head ) do
            if glyph_node.data == id then
                counter = counter + 1
                local tail_node = TAIL ( n.head )
                local glue_node = NEW ( GLUE )
                glue_node.subtype = SPACESKIP
                glue_node.width = WIDTH
                local NEXT
                local switch_counter = 1 -- page_counter
                n.head = INS_A ( n.head, TAIL ( n.head ), glue_node )
                if ( switch_counter % 2 == 0 ) then
                    NEXT = glue_node
                else
                    NEXT = tail_node
                end
                local kern_value = 0
                for _, value in ipairs ( array[counter] ) do
                    if value ~= false then
                        local NUMBER = COPY ( value )
                            n.head = INS_A ( n.head, NEXT, NUMBER)
                            if NEXT.next then
                                NEXT = NEXT.next
                            end
                        if NUMBER.width then
                            kern_value = kern_value - NUMBER.width
                        end
                    end
                end
                local kern_node = NEW ( KERN )
                kern_node.kern = kern_value - glue_node.width
                if switch_counter % 2 ~= 0  then
                    kern_node.kern = kern_node.kern - tex.hsize + first_kern
                    n.head = INS_A ( n.head, tail_node, kern_node )
                end
                if ( switch_counter % 2 == 0 ) and ( first_kern < 0 ) then
                    kern_node.kern = kern_node.kern - first_kern + first_width - kern_value
                    n.head = INS_A ( n.head, tail_node, kern_node )
                end
                first_kern = kern_node.kern
                first_width = kern_value
            end
        end
    end
    return head, counter
end

local function make_text_notes ( head )
    page_counter = page_counter + 1
    head, p_counter_x = make_margin_notes ( head, 427956, p_array, p_counter_x )
    return head
end

    ATC ( "ligaturing", mark_notes , "mark notes" )
    ATC ( "pre_output_filter", make_text_notes , "count pages" )

\end{luacode}

\flushbottom

\pagestyle{empty}

\usepackage{showkerning}

\RedeclareSectionCommand[%
    afterskip=1.3ex plus .2ex,%
    beforeskip=-2.5ex plus -1ex minus -.2ex,%
    font=\superlarge%
]%
{section}

\begin{document}

\directlua{
    local function rem_kern ( head )
        for n in node.traverse ( head ) do
            if n.id == node.id ( "hlist" ) or n.id == node.id ( "vlist" ) then
                n.head = rem_kern ( n.head )
            elseif n.id == node.id ( "glyph" ) then
                if n.char == 112 then
                    n.prev.data = ""
                end
            end
        end
        return head
    end

    luatexbase.add_to_callback ( "post_linebreak_filter", rem_kern, "remove kern", 1 )
}

\title{The showk\kern-.1eme\kern.2emrn\kern-.05emin\kern.1emg package\vspace{.25\baselineskip}\\\superlarge{}\directlua{luatexbase.remove_from_callback ( "post_linebreak_filter", "show kerns in postline" ) luatexbase.remove_from_callback ( "hpack_filter", "show kerns in hpack" ) luatexbase.remove_from_callback ( "post_linebreak_filter", "remove kern" )}Showing kerns in a document}%
\author{\sublarge{}Thomas Kelkel\vspace{-.25\baselineskip}\\\sublarge{}kelkel@emaileon.de\vspace{-.25\baselineskip}}%
\date{\addfontfeature{LetterSpace=2}\sublarge{}2022/05/31\quad{}v0.1}%
\maketitle

\thispagestyle{empty}

\section{Introduction}

This package displays all kerning values in the form of colored bars directly at the respective position in the document. Positive values are displayed in green, negative values in red. The width of the bars corresponds exactly to the respective kerning value. The left edge of the bar is always at the position where the kerning node is placed. (This corresponds to the common representation method).

Please note that Lua{\addfontfeature{LetterSpace = 2}\LaTeX} is required to use this package.

\section{Basic usage}

To load the package, simply add the following line to the preamble of the document:

\begin{quote}
    \mono{\textbackslash{}usepackage\{showkerning\}}
\end{quote}

\section{Package options}

\addcontentsline{toc}{subsection}{ontop}

\textnote{ontop}By default, the bars are placed behind the glyphs. With this option they are in front of them. It can be loaded in the following way:

\begin{quote}
    \mono{\textbackslash{}usepackage[ontop]\{showkerning\}}
\end{quote}

\section{License}

This package is copyright © 2022 Thomas Kelkel. It may be distributed and/or modified under the conditions of the LaTeX Project Public License, either version 1.3c of this license or (at your option) any later version. This work has the LPPL maintenance status \qq{author maintained}.

\end{document}