csquotes: Using Auto Quotes to Create Block Quotes if Required

Question

One of the great features of csquotes is that, using \MakeAutoQuote, we can simply type proper hard-coded quotation marks and have csquotes do the rest, i.e. turn them into the correct format (as defined by language, typography etc.), plus take care of nesting:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[english]{babel}
\usepackage[babel]{csquotes}
\usepackage{lipsum}

\MakeAutoQuote{»}{«}
\MakeAutoQuote*{›}{‹}

\begin{document}
\lipsum*[1]
»\lipsum*[2] »[...]««
\lipsum*[3]
\blockquote{\lipsum*[2] »[...]«}
\end{document}

In my documents, I use » + « and › + ‹ exclusively (placed on an easy-to-reach position on my keyboard), no matter what language I'm writing in, no matter what the quotation marks are required to look like in print. Csquotes will treat them as \enquotes. That's perfect ...unless we're talking about a longer quote which we'd like to automatically be turned into block format. What I'd like to have is an even smarter autoquote that behaves like \blockquote rather than \enquote, i.e. that will switch to block format if the anticipated length hits a certain threshold. That way, I could uniformly use » and « throughout my document without having to manually consider the quote's length.

Unfortunately, \MakeAutoQuote seems to be linked to \enquote rather tightly (§4.1 of csquotes doc). What would be a way of changing that, and are there any pitfalls that I'm not aware of at the moment?

FOLLOW-UP

prompted by @cfr's and Ulrike's replies, I came up with (the idea of) what some might consider a somewhat dirty workaround. If we can use \mkblockquote to define the block quotes' precise format, why not change the function of our active blockquoting chars (e.g. » and «) after the beginning of each instance of a block quote -- to become active textquoting chars inside the block quote? And give them back their block quote function at the very end?

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[english]{babel}
\usepackage[babel]{csquotes}
\usepackage{lipsum}

% define » and « to trigger a block quote
\MakeBlockQuote{»}{|}{«}

\renewcommand{\mkblockquote}[4]{%
% inside a block quote, make them trigger a text quote
\MakeAutoQuote{»}{«}%
#1#2#3#4%
% now they resume functioning as block quote triggers again
\MakeBlockQuote{»}{|}{«}
}%

\begin{document}
\lipsum*[1]
»\lipsum*[2]«
»\lipsum*[2] »[...]««
\lipsum*[3]

\end{document}

Apparently, this is not how it works. I had hoped \MakeBlockQuote would work like, say, \renewcommand, but csquotes doesn't seem to accept a re-definition of the active blockquote chars. Even this construction causes an »invalid argument error«:

\MakeBlockQuote{»}{|}{«}
\MakeBlockQuote{>}{|}{<}

It's as if, once defined, the block quotes are inseperably tied to those chars. Or is there a way we can make this work somehow?

Answer 1

Maybe I'm missing something but why not define your active characters to use \MakeBlockQuote instead? I guess this doesn't allow you to specify inner/outer marks specifically but if csquotes is taking care of the nesting in any case, perhaps that is not too much of a problem. (I define both outer and inner but never actually use the inner ones for just this reason.)

\documentclass[british]{article}
\usepackage{babel}
\usepackage[utf8]{inputenc}
\usepackage{csquotes}
\usepackage{kantlipsum}
\MakeBlockQuote{<}{|}{>}
\begin{document}

  \kant[2]
  <\kant[1]>

  \kant[3]

  Some more text. <This is a short quote.>
  `This is another short quote.'

\end{document}

The final short quote is just for purposes of comparison.

EDIT

Ulrike Fischer has pointed out that you cannot nest block quotations with csquotes (but you can nest regular LaTeX block quotations).

What you can do is combine the above method with the use of regular active quote characters and csquotes will figure out the nesting correctly. Whether this is a significant limitation or not probably depends on the kind of work you do. If you regularly need to typeset block quotations which include other block quotations, it will obviously not be a good solution. If that is a relatively rare occurrence, perhaps not so much.

\documentclass[british]{article}
\usepackage{babel}
\usepackage[utf8]{inputenc}
\usepackage{csquotes}
   \MakeAutoQuote{‘}{’}
   \MakeAutoQuote*{“}{”}
\usepackage{kantlipsum}
\MakeBlockQuote{<}{|}{>}
\begin{document}

  \kant[2]
  <\kant[1]>

  \kant[3]

  Some more text. <This ‘is’ a short quote.>
  `This is another short quote.'

\end{document}