Angle brackets and parentheses are just two of the many flavors of brackets you'll find in MDL. First, you got your regular, "boring" brackets:

  <SETG X 0>           ;FORM
  (NORD BERT)          ;LIST
  [1 MONEY 2 SHOW]     ;VECTOR
  "Bracket-ish"        ;STRING
  { what goes here? }  ;TEMPLATE

Then you got your exciting brackets, where the first ! is mandatory but the second is optional:

  !<REST .FOO!>        ;SEGMENT
  ![2 4 8 16 32 64!]   ;UVECTOR

Then you got your hashtag brackets, which pop up in the corner of the TV screen reminding you that there's another way to CHTYPE:

  #FORM (+ 1 2)        ;"same as <+ 1 2>"

And your hashtag voucher brackets, which are really just defective angle brackets you can exchange for a free hashtag:

  <>                   ;"evaluates to #FALSE ()"

Finally, you got your bogus brackets, things that look like they could be a new kind of exciting brackets, but when you look closely they're just prefix operators that tend to appear before brackets:

  '(OSCAR WILDE)       ;"same as <QUOTE (OSCAR WILDE)>"
  %<+ 1 2>             ;"evaluate immediately"
  %%<CRLF>             ;"evaluate and discard result"

See also: https://github.com/taradinoc/mdl-docs/blob/master/docs/07-st...