{
    "elmType": "div",
    "txtContent": "[$customField]"
}

{
    "elmType": "div",
    "txtContent": "[$FileLeafRef]"
}

{
    "elmType": "div",
    "txtContent": "[$File_x0020_Type]"
}

{
    "elmType": "div",
    "txtContent": "[$SomeParentTextColumn]"
}

{
    "elmType": "div",
    "txtContent": "[$Title]"
}
{
    "elmType": "div",
    "txtContent": "[$SomeParentChoiceColumn]"
}