$ forester init > /dev/null

  $ cat > trees/index.tree << EOF
  > \def\my-object{
  >   \object[self]{
  >     [method1]{
  >       \p{Hello method1}
  >     }
  >   }
  > }
  > \my-object#method1
  > EOF

  $ forester build > /dev/null

  $ grep -o 'Hello method1' output/index/index.html
  Hello method1

Unfortunately, the error message here is pretty bad, since the error only
occurs when the top-level `extract_content` is called, to which the total range
is associated. Thus the error has as the location the entire file. I think
improving this will require rearchitecting the evaluator.

  $ cat > trees/index.tree << EOF
  > \def\my-object{
  >   \object[self]{
  >     [method1]{
  >       \p{Hello method1}
  >     }
  >   }
  > }
  > \patch{\my-object}[self]{
  >   [method1]{}
  > }
  > EOF

  $ forester build
  error[type_mismatch]: mismatched type
      ┌─ $TESTCASE_ROOT/trees/index.tree:1:1
    1 │ ╭  \def\my-object{
    2 │ │    \object[self]{
    3 │ │      [method1]{
    4 │ │        \p{Hello method1}
      · │  
    7 │ │  }
    8 │ │  \patch{\my-object}[self]{
    9 │ │    [method1]{}
   10 │ │  }
      │ ╰───^ This is an object. Did you forget to bind this object to an identifier?
   11 │    
      = expected some content
  [1]