[pracjourn-forum] For our error collection

[Karl Berry]

    would be useful to have help for cases where (as here) the error
    message is cryptic

It occurred to me that in this case the problem could be fixed without
changing the TeX binary (or LaTeX) at all:

\let\realcolon=\:
\def\:{\ifmmode\realcolon\else
         \errmessage{You must be in math mode to use \: ...}\errhelp{...}}

Perhaps the LaTeX folks would be willing to consider a patch that
changes \: in such a way, if anyone wants to pursue it.

I don't know how many cases can be fixed like this.  If there are a lot,
a package could be constructed.  We need more data points.

    And, if it's up on CTAN, 

CTAN doesn't normally mirror web pages AFAIK, but I can make it
accessible by ftp if it turns to be desirable, as Jim implies.

    we could solicit other examples

We can solicit other examples no matter what, but I think we need to
finish a framework and introduction before publicizing it.

k