Comment by MawKKe

why not go further, why can't we just write

  <tree
    <leaf colour="green">
    <leaf colour="yellow">
  >

although now that ="foo" business seems too noisy. how about

  <tree
    <leaf :colour green>
    <leaf :colour yellow>
  >

also, those angle brackets are too pointy, let's swap them to something more pleasant

   (tree
     (leaf :colour green)
     (leaf :colour yellow))