Div block syntax

Extensions
2

See also: https://talk.commonmark.org/t/content-block-inline-syntax/815.

I note from that thread that there was some interest in using ::: to delimit blocks. I think that proposal loses traction because those colons don’t make a very attractive horizontal delimeter, but I think the general idea of using the top line as a header with “{.styling}” info is good.

Example from that thread, using above div syntax (both side-marked and delimited):

::::::::::::::::::::::: WARNING  ::::::::::::::::::::::::::::
            # rm -rf / – Deletes Everything! #

  The command rm -rf / deletes everything it possible can,
 including files on your hard drive and files on connected 
                 removable media devices. 
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

vs.

; ------------------------------------------------- {.warning}
            # rm -rf / – Deletes Everything! #

The command rm -rf / deletes everything it possible can,
including files on your hard drive and files on connected 
removable media devices. 
; -----------------------------------------------------------

and

; ------------------------------------------------- {.warning}
;           # rm -rf / – Deletes Everything! #
;
; The command rm -rf / deletes everything it possible can,
; including files on your hard drive and files on connected 
; removable media devices.