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 800x88
  LayoutBlockFlow {html} at (0,0) size 800x88
    LayoutBlockFlow {body} at (8,16) size 784x56
      LayoutBlockFlow {p} at (0,0) size 784x20
        LayoutText {#text} at (0,0) size 218x19
          text run at (0,0) width 218: "You should see error text above this"
      LayoutBlockFlow (anonymous) at (0,36) size 784x0
        LayoutInline {bar} at (0,0) size 0x0
      LayoutBlockFlow {p} at (0,36) size 784x20
        LayoutText {#text} at (0,0) size 331x19
          text run at (0,0) width 331: "ERROR? this, and nothing below it should be rendered"