How to add taxonomy element to a summary view?

[re: Orchard CMS]

This caused me scratching my head for days and now I can even feel it's bleeding.

The answer however is the simplest.

Because it's not obviously indicated anywhere, I was anticipating the layout only works for the detail view of A content item.

The trueth is not. Add this in the placement.info and you get the element in the summary view:

  <Match DisplayType="Summary">
    <Place Parts_Layout="Content:10"/>
  </Match>

This post assumes you've played with the layout feature for a while.