> \starttext
>
> A few years back, \TEX\ could only produce
> \fillinfield [dvi]{\DVI} output,
> but nowadays, thanks to \fillinfield {Han The Thanh}, we can also
> directly produce \fillinfield [pdf] {\PDF}!
> Nice eh? Actually, while the first field module was prototyped
> in \ACROBAT, the current implementation was debugged in
> \fillinfield [pdfTeX] {\PDFTEX}. Field support in \fillinfield
> [ConTeXt] {\CONTEXT} is rather advanced and complete and all
> kind of fields are supported. One can hook in appearances, and
> validation \fillinfield [JavaScripts] {\JAVASCRIPT}’s. Fields
> can be cloned and copied, where the latter saves some space. By
> using \fillinfield {objects} when suited, this module saves
> space anyway.
>
> \stoptext
>
> But I get:
> mtx-context     | run 1: luatex
> --fmt="/home/cecil/ConTeXt/tex/texmf-cache/luatex-cache/context/5fe67e0bfe781ce0dde776fb1556f32e/formats/cont-en"
> --lua="/home/cecil/ConTeXt/tex/texmf-cache/luatex-cache/context/5fe67e0bfe781ce0dde776fb1556f32e/formats/cont-en.lui"
> --backend="pdf" "./test"
> This is LuaTeX, Version beta-0.65.0-2010121316
>  \write18 enabled.
> (test.tex
>
> ConTeXt  ver: 2011.03.27 14:48 MKIV  fmt: 2011.3.27  int: english/english
>
> system          > cont-new.mkiv loaded
> (/home/cecil/ConTeXt/tex/texmf-context/tex/context/base/cont-new.mkiv
> system          > beware: some patches loaded from cont-new.mkiv
> )
> system          > test.top loaded
> (test.top)
> fonts           > latin modern fonts are not preloaded
> languages       > language en is active
> {/home/cecil/ConTeXt/tex/texmf-context/fonts/map/pdftex/context/mkiv-base.map}
> fonts           > preloading latin modern fonts (second stage)
> (/home/cecil/ConTeXt/tex/texmf-context/tex/context/base/type-siz.mkiv)
> (/home/cecil/ConTeXt/tex/texmf-context/tex/context/base/type-otf.mkiv){/home/cecil/ConTeXt/tex/texmf/fonts/map/dvips/lm/lm-math.map}{/home/cecil/ConTeXt/tex/texmf/fonts/map/dvips/lm/lm-rm.map}
> fonts           > virtual math > unable to resolve name mapsfromchar
> fonts           > fallback modern rm 12pt is loaded
> system          > begin file test at line 1
> ! Undefined control sequence.
>
> system          > tex > error on line 4 in file test.tex: Undefined
> control sequence ...
>

> I tried the first example from fill-in fields:
\def\DVI{DVI}
\def\PDF{PDF}
\def\ACROBAT{Acrobat}
\def\JAVASCRIPT{Javascript}

>  1     \starttext
>  2
>  3     A few years back, \TEX\ could only produce
>  4 >>  \fillinfield [dvi]{\DVI} output,
>  5     but nowadays, thanks to \fillinfield {Han The Thanh}, we can also
> directly produce \fillinfield [pdf] {\PDF}!
>  6     Nice eh? Actually, while the first field module was prototyped
>  7     in \ACROBAT, the current implementation was debugged in
>  8     \fillinfield [pdfTeX] {\PDFTEX}. Field support in \fillinfield
>  9     [ConTeXt] {\CONTEXT} is rather advanced and complete and all
> 10     kind of fields are supported. One can hook in appearances, and
> 11     validation \fillinfield [JavaScripts] {\JAVASCRIPT}’s. Fields
> 12     can be cloned and copied, where the latter saves some space. By
> 13     using \fillinfield {objects} when suited, this module saves
> 14     space anyway.
>
> l.4 \fillinfield
>                  [dvi]{\DVI} output,
>
> What is happening here?
>

I guess Hans has removed some obsolete definitions :-)