\setupbodyfont[dejavu]

\startluacode
    fonts.handlers.otf.addfeature {
        name    = "chaintest",
        type    = "chainposition",
        lookups = {
            {
                type = "pair",
                data = {
                    A = { B = { { -30, 0, -50, 0 } } },
                    B = { C = { { -30, 0, -50, 0 } } },
                },
            },
            {
                type = "pair",
                data = {
                    D = { E = { { -30, 0, -50, 0 } } },
                },
            },
        },
        data = {
            rules = {
                {
                    current = { { "A"}, { "B"}, { "C" }, { "D" }, { "E" }, { "F" } },
                    lookups = { false, false, false, 2 },
                },
                {
                    current = { { "A" }, { "B" }, { "C" } },
                    lookups = { 1, 1 },
                },
            },
        }
    }
\stopluacode

\starttext

\definecolor[tgray][s=.5,t=.5,a=1] \showfontkerns \showglyphs

\definefontfeature[chaintest] [mode=node,chaintest=yes]

\definedfont[file:dejavu-serif.ttf*chaintest @ 48pt]

\startTEXpage[offset=10pt,foregroundcolor=tgray]
    ABCDEF
\stopTEXpage

\stoptext