\showframe

% \enabletrackers[mixedcolumns.*]

\starttext

    \startmixedcolumns[n=4]
    \stopmixedcolumns

    \startmixedcolumns[n=4]
        \blank first \column
    \stopmixedcolumns

    \startmixedcolumns[n=4]
        \blank first \column
        \blank first \column
    \stopmixedcolumns

    \startmixedcolumns[n=4]
        \blank first \column
        \blank first
    \stopmixedcolumns

    \startmixedcolumns[n=4]
        \blank second \column
        \blank second \column
        \blank second \column
        \blank second
    \stopmixedcolumns

    \startcolumns[n=4]
        \blank third \column
        \blank third \column
        \blank third \column
        \blank third
    \stopcolumns

\stoptext
