User blog comment:Vel!/Symbols function/@comment-5029411-20121221235825/@comment-25371339-20140926192739

Extension:

[<[+++...+++]>]+++...+++ = ...[ [+++...+++] ]... with n brackets

[<[ [+++...+++] ]>]+++...+++ = [<[+++...+++]>][<[+++...+++]>][<[+++...+++]>]...[<[+++...+++]>][<[+++...+++]>][<[+++...+++]>] with n 2-level brackets

[<[<[+++...+++]>]>]+++...+++ = ...[ [+++...+++] ]... [<...[ [+++...+++] ]...>] with n brackets

etc.