$ forester init > /dev/null

  $ cat > trees/index.tree << EOF
  > \p{
  >   \<foo:bar>
  > }
  > EOF

  $ forester build
  error[unresolved_xmlns]: Unresolved XML namespace
      ┌─ $TESTCASE_ROOT/trees/index.tree:2:4
    2 │    \<foo:bar>
      │     ^^^^^^^^^ 
      = expected "foo" to resolve to an XML namespace
      = You may fix this by defining an XML namespace:
        \xmlns:foo{...}
  [1]