(pdfe)TeX register clash?

["F. Miller Maley" <maley@idaccr.org>]

I'm using ConTeXt with pdfeTeX to typeset a large manuscript, and things
have been going very well, but I had to work around the following problem.

When I defined variables using the plain TeX methods, e.g.

\newcount\Mycount
\newbox\Mybox

and started using these in my macros, it seemed to confuse ConTeXt about
which pages were left pages and which were right pages.  If I just blindly
say

\chardef\Mycount=200
\chardef\Mybox=200

then everything works.  It seems ConTeXt and I were using the same counter.

What is the preferred method for allocating variables (TeX registers) for
my own macros?  My apologies if this is a FAQ.  I couldn't find a FAQ file
for this mailing list.

By the way, I am using the (undocumented?) option \setuparranging[2SIDE].

-- Miller Maley