Just three completely undocumented syntax examples...

Mapping values in an object:

    {a, b} = c

Backslash to continue lines:

    a = long_variable_name \
      + other_long variable name

Switch statements without a parameter:

    switch
      when function_that_needs_to_return_true
        stuff

But the bigger problem is just having no idea how things will parse. For example, this works:

    a = b +
      c

But this doesn't:

    a = b
      + c

And then this works:

    switch a
      when b, c, d
        e()

But this doesn't (a multi-line form you might want to use if the variable names were really long):

    switch a
      when b, 
          c,
          d
        e()

And this doesn't:

    switch a
      when b
      when c
      when d
        e()

After trial-and-error, you discover it has to be this, with a seemingly random backslashes:

    switch a
      when b, \
          c, \
          d
        e()

I could go on and on -- but you get the point. The whole language is only discoverable via trial and error. None of this is documented. (Apologies for taking up so much vertical space of the comments!!)