\starttext
\startblockquote
[w]hile we may

[w]hile we may

\stopblockquote
\stoptext

seems to fail with the latest beta (ConTeXt  ver: 2016.10.14) unless one replaces the first line with
\[w\]hile we may.

The error message is
tex error       > tex error on line 4 in file /Users/bowen1/Desktop/TestTeX/test.tex: ! Missing number, treated as zero

<to be read again> 
w
\spac_narrower_method_analyze ...arrower_middle #1
                                                  \relax \fi 
\syst_helpers_repeat_with_command ..._again [#1]#5
                                                  \else \syst_helpers_repeat...
\17>>1 ..._process_comma_list_with_parameters {#1}
                                                  \syst_helpers_do_process_c...
\syst_helpers_do_process_comma_list ...rgument #1,
                                                  ]\relax \global \advance \...
\spac_narrower_start_apply ...narrower_initialize 
                                                  \advance \leftskip \dimexp...
...
l.4 [w]h
      ile we may

 1     \starttext
 2     
 3     \startblockquote
 4 >>  [w]hile we may
 5     
 6     [w]hile we may
 7     
 8     \stopblockquote
 9     
10     \stoptext
11     


? 


Alan