Single-line comments begin with a # symbol and extend to the end of the line:

# This is an example of a single-line, standalone comment
fun example(n):
  1 + n # This single-line comment starts after some code
end

Block comments begin with a #| symbol and end with a matching |#.

fun example(n):
  #|
     This comment can extend
     over multiple lines
  |#
  1 + n
end

While the text of a comment block contains everything between the #| and |# symbols, it is preferred to put them on their own lines, so they are visually distinctive and can easily be added or removed:

#|
  prefer this
  style
|#

#| instead of
   this style |#

The one exception is when block comments are being used to comment out sections of a single line of code:

rectangle(30 #|width|#, 40 #|height|#, "solid", "red")

They can be nested within each other, so long as the delimiters are matched:

fun example(n):
  #| this is in a comment
     #| so is this
        and this
     |#
     and this
  |#
  1 + n
end

fun example(n):
  #| This is a block comment.
     Even though the next line starts a single-line comment
     # the block-comment ends here |#
  1 + n
end

(Naturally, this style isn’t preferred, as it is easy to ignore the end-of-comment marker when reading quickly!)