I've noticed that ,doc fcollect produces weirdly indented documentation:

>> ,doc fcollect
(fcollect iter-tbl value-expr ...)
  Return a sequential table made by advancing a range as specified by
      for, and evaluating an expression that returns values to be inserted
      sequentially into the table.  This can be thought of as a range
      comprehension. If the body evaluates to nil that element is omitted.
      
      For example,
        (fcollect [i 1 10 2]
          (when (not= i 3)
            (* i i)))
      returns
        [1 25 49 81]
      
      Supports an &into clause after the range to put results in an existing table.
      Supports early termination with an &until clause.
>> 

This happens both in an ordinary terminal, and in Emacs repls.

This happens to a lot of forms, but not for all of them:

>> ,doc lambda
(lambda ...)
  Function literal with nil-checked arguments.
      Like `fn`, but will throw an exception if a declared argument is passed in as
      nil, unless that argument's name begins with a question mark.
>> ,doc fn
(fn name? args docstring? ...)
  Function syntax. May optionally include a name and docstring or a metadata table.
  If a name is provided, the function will be bound in the current scope.
  When called with the wrong number of args, excess args will be discarded
  and lacking args will be nil, use lambda for arity-checked functions.
>>

Upon further inspection it turned out that the reason for that is that fennel.lua has these macros stored in a giant string, and that indentation is preserved when this string is evaluated, adding additional two spaces. Specials, such as fn on the other hand, store their documentation in a spearate place, and it has the correct indentation.