In my use case a KM Macro writes a text-file in the widget folder, and then this gets displayed.
This is the code in the widget. The refresh interval is large, since the KM macro ends with forcing Übersicht to refresh the widget.
command: "cat order-data.widget/order-data.txt"
refreshFrequency: 100000000
render: (output) ->
"<pre><div class='orderdata'>#{output}</div></pre>"
style: """
left: 55px
top: 450px
color: #fff
width: 430px
height: 200px
font-family: Menlo
.orderdata
display: block
background: rgba(#000, 0.2)
border-radius: 0px
font-size: 18px
font-weight: 300
padding: 4px 6px 4px 6px
&:after
content: 'Order data'
position: absolute
left: 10px
top: 0px
font-size: 12px
font-weight: 700
font-family: -apple-system
"""