* The colon modifier can now occur 2 times.
  Specifying `@` more than once or `:` more than twice is an error now.
* Commands do not check for excess colon modifiers - almost every command would have
  to check it. Instead, a double colon will simply behave like a single colon on most
  commands.
* All search commands inherit the anchored semantics, but it's not very useful in some combinations
  like -::S, ::N or ::FK.
  That's why the `::` variants are not documented everywhere.
* The lexer.checkheader macro could be simplified and should also be faster now,
  speeding up startup.
  Eventually this macro can be made superfluous, e.g. by using 1:FB or 0,1^Q::S.

* Can be freely combined with the colon-modifier as well.
  :@Xq cut-appends to register q.
* This simply deletes the given buffer range after the copy or append operation
  as if followed by another <K> command.
* This has indeed been a very annoying missing feature, as you often have to retype the
  range for a K or D command.
  At the same time, this cannot be reasonably solved with a macro since macros
  do not accept Q-Register arguments -- so we would have to restrict ourselves to one or a few
  selected registers.
  I was also considering to solve this with a special stack operation that duplicates the
  top values, so that Xq leaves arguments for K, but this couldn't work for cutting lines
  and would also be longer to type.
* It's the first non-string command that accepts @.
  Others may follow in the future.
  We're approaching ITS TECO madness levels.

* We cannot call it "." since that introduces a local register
  and we don't want to add an unnecessary syntactic exception.
* Allows the idiom [: ... ]: to temporarily move around.
  Also, you can now write ^E\: without having to store dot in a register first.
* In the future we might add an ^E register as well for byte offsets.
  However, there are much fewer useful applications.
* Of course, you can now also write nU: instead of nJ, Q: instead of "." and
  n%: instead of "nC.". However it's all not really useful.

* This way the search mode and radix are local to the current macro frame,
  unless the macro was invoked with :Mq.
  If colon-modified, you can reproduce the same effect by calling
  [.^X 0^X ... ].^X
* The radix register is cached in the Q-Reg table as an optimization.
  This could be done with the other "special" registers as well, but at the
  cost of larger stack frames.
* In order to allow constructs like [.^X typed with upcarets,
  the Q-Register specification syntax has been extended:
  ^c is the corresponding control code instead of the register "^".

* also explicitly mention -%q