CONSOLE ERROR: line 8: Namespace prefix foo on bar is not defined

layer at (0,0) size 800x600
  LayoutView at (0,0) size 800x600
layer at (0,0) size 800x84
  LayoutBlockFlow {html} at (0,0) size 800x84
    LayoutBlockFlow {body} at (8,16) size 784x52
      LayoutBlockFlow {p} at (0,0) size 784x18
        LayoutText {#text} at (0,0) size 232x17
          text run at (0,0) width 232: "You should see error text above this"
      LayoutBlockFlow (anonymous) at (0,34) size 784x0
        LayoutInline {bar} at (0,0) size 0x0
      LayoutBlockFlow {p} at (0,34) size 784x18
        LayoutText {#text} at (0,0) size 354x17
          text run at (0,0) width 354: "ERROR? this, and nothing below it should be rendered"