ConTeXt: Macro to get character width

Question

Background

Looking to adjust the location of the first letter in a word based on its width.

Problem

The calculation resembles:

\define[1]\StyleChapterChar{%
  \cldcontext{string.sub("#1",1,1)}%
}

% Use a nested frame to keep the overlain large letter together with
% the chapter title.
\define[1]\StyleChapter{%
  \StyleChapterFramed{%
    \framed[align=right, frame=off]{%
      \startoverlay
        \color[blue]{%
          \StyleChapterChar{#1}%
        }
        \vskip-1.9em\hskip\dimexpr\averagecharwidth*33/10#1
      \stopoverlay
    }
  }
}

Here, 3.3 * \averagecharwidth is used to offset the text. This causes the horizontal offset of the emphasized first character in the word to vary wildly between an A and an I. What I would like is to replace this calculation (3.3 * \averagecharwidth) with one that uses the character width (e.g., 3.3 * \charwidth{\StyleChapterChar})

Question

How do you get the width of a single character, when you don't know what that character is?

Ideas

I've tried a few things so far:

\define[1]\StyleChapterCharWidth{
  \dimexpr\fontcharwd\font`#1
}

\define[1]\StyleChapterCharWidth{
  \fontcharwd\font`#1
}

It seems like the back-tick (`) character indicates that the next character should be treated literally.

Related

• https://gitorious.org/context/context/source/8e052e94b8b3ca08900ab4fe0a5bf110f6a52327:tex/context/base/lang-frq.mkii
• Determine width of verbatim characters
• How to set the width of the label of a description to the width of a string of text in ConTeXt?

Answer 1

Using Aditya's clue:

\define[1]\StyleChapterChar{%
  \cldcontext{string.sub("#1",1,1)}%
}

\define[1]\StyleChapter{%
  \StyleChapterFramed{%
    \framed[align=right, frame=off]{%
      \startoverlay
        % Calculate the offset of the large letter based on the width of
        % the character. This allows the font to change without significantly
        % affecting the distance between the emphasized first character of the
        % chapter title and the complete chapter title.
        \setbox\scratchbox\hbox{%
          \StyleFontChapterCharacter\StyleChapterChar{#1}}%
        % Shift the first character back relative to the chapter title.
        \hskip-.55\wd\scratchbox%
        \color[blue]{%
          \StyleFontChapterCharacter%
          \StyleChapterChar{#1}%
        }
        \vskip-1.9em
        #1
      \stopoverlay
    }
  }
}