ConTeXt  ver: 2008.07.10 08:40 MKIV  fmt: 2008.7.10  int: english/english

See test.tex in attachement.

The following combinations give the following results after compiling with

   texmfstart texexec --lua test.tex

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(1) \definefont[myChapterFont][myHeadingsFont sa 1.728]  % with

\setuphead[chapter][style=myChapterFont] % or
\setuphead[chapter][style=\myChapterFont] % or
\setuphead[chapter][style={\myChapterFont}]

generates the following compile error...

! Font \**myChapterFont**:=myHeadingsFont at 20.736pt not loadable: metric
data not found or bad.
<to be read again>
                   \relax
\dododefinefont ...ontspec {#2}\rawfontidentifier
                                                  \let
\localrelativefontsiz...
\dosetfontattribute ...me #1#2\@EA \endcsname \fi
                                                  \empty
\doplaceheadnumbertext ...bute {\??ko #1}\c!style
                                                  \getvalue {\??ko
#1\c!comm...
\dodododoconstructhead ...{\finalsectionnumber }}}
                                                  \writesection
{#1}{#3}{#4}...
l.54 \chapter{chapter test}

?
! Emergency stop.
<to be read again>
                   \relax
\dododefinefont ...ontspec {#2}\rawfontidentifier
                                                  \let
\localrelativefontsiz...
\dosetfontattribute ...me #1#2\@EA \endcsname \fi
                                                  \empty
\doplaceheadnumbertext ...bute {\??ko #1}\c!style
                                                  \getvalue {\??ko
#1\c!comm...
\dodododoconstructhead ...{\finalsectionnumber }}}
                                                  \writesection
{#1}{#3}{#4}...
l.54 \chapter{chapter test}

!  ==> Fatal error occurred, no output PDF file produced!

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(2) \definefont[myChapterFont][Sans sa 1.728]  % with

\setuphead[chapter][style=myChapterFont] % or
\setuphead[chapter][style=\myChapterFont] % or
\setuphead[chapter][style={\myChapterFont}]

displays the chapter heading with a scaled LMSans10-Regular font

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(3) this displays the chapter heading font correctly

\setuphead[chapter][style={\tfc\myHeadingsFont}]

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(4) \setuphead[chapter][style={\tfc\Sans}]

generates the following compile error...

! Undefined control sequence.
\@@kochapterstyle ->\tfc \Sans

\doifdefinedelse #1->\edef \p!defined {#1
                                         }\ifcsname \detokenize \@EA
{\p!def...
\doconvertfont #1->\doifdefinedelse {\@letter@ #1}
                                                   {\doifelsenothing
{#1}\go...
\dosetfontattribute ...me #1#2\@EA \endcsname \fi
                                                  \empty
\doplaceheadnumbertext ...bute {\??ko #1}\c!style
                                                  \getvalue {\??ko
#1\c!comm...
\dodododoconstructhead ...{\finalsectionnumber }}}
                                                  \writesection
{#1}{#3}{#4}...
l.54 \chapter{chapter test}

?
! Emergency stop.
\@@kochapterstyle ->\tfc \Sans

\doifdefinedelse #1->\edef \p!defined {#1
                                         }\ifcsname \detokenize \@EA
{\p!def...
\doconvertfont #1->\doifdefinedelse {\@letter@ #1}
                                                   {\doifelsenothing
{#1}\go...
\dosetfontattribute ...me #1#2\@EA \endcsname \fi
                                                  \empty
\doplaceheadnumbertext ...bute {\??ko #1}\c!style
                                                  \getvalue {\??ko
#1\c!comm...
\dodododoconstructhead ...{\finalsectionnumber }}}
                                                  \writesection
{#1}{#3}{#4}...
l.54 \chapter{chapter test}

!  ==> Fatal error occurred, no output PDF file produced!

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How come ?

Alan