If \thinrule is used in \margintext, context gives error. \hairline 
works fine.


*Details:* ConTeXt  ver: 2013.01.10 01:04 MKIV  fmt: 2013.1.13

*Error Message:*
! Undefined control sequence.

system          > tex > error on line 2 in file a.tex: Undefined control 
sequence ...

1     \starttext
2 >>  \margintext{\thinrule A margintext with thinrule.}
3     %\margintext{\hairline A margintext with hairline.}
4     \stoptext
5


\thinrule ->\strut \bgroup \edef \p_height
{\directthinrulesparameter \c!hei...
<argument> \thinrule
                      A margintext with thinrule.
\doifelsenothing #1->\edef \m_syst_string_one {#1
                                                  }\ifx 
\m_syst_string_one \e...
\typo_margins_data_yes_indeed ...felsenothing {#3}
                                                   \donefalse \donetrue 
\ifdo...
l.2 ...text{\thinrule A margintext with thinrule.}


**MWE**

\starttext
%\margintext{\thinrule A margintext with thinrule.}
\margintext{\hairline A margintext with hairline.}
\stoptext