[Tex/LaTex] hyphenation: what special is in word “implementation”

hyphenation

What special is in the word "implementation" that it is not possible automatic hyphenate in narrower environments as are minipage, TikZ nodes etc, even if in preamble is added hyphenation pattern for it?

Interestingly, hyphenation works, if in the begins of those environments is added \hspace{0pt}! Examples:

\documentclass{article}
\begin{document}

\textbullet doesn't work:

    \smallskip
\fbox{\begin{minipage}{4em}
        implementation
      \end{minipage}
      }

\medskip
\textbullet\ with use of \verb+\hspace*{0pt}+ works:

\fbox{\begin{minipage}{4em}\hspace*{0pt} % <---
        implementation
      \end{minipage}
      }
\end{document}

enter image description here

And example at use TikZ nodes:

    \documentclass{article}
    \usepackage{tikz}
    \begin{document}

    \textbullet\ doesn't work:

    \smallskip
    \tikz\node[draw, text width=4em, align=center] {implementation};

     \textbullet\ with use of \verb+\hspace*{0pt}+ works:

    \tikz\node[draw, text width=4em, align=center,
               execute at begin node=\hspace*{0pt}] % <---
               {implementation};
    \end{document}

enter image description here

I wonder, what is in the word implementation. For example, with similar long word hyphenation this problem not occur.

Best Answer

There is nothing special about implementation. TeX simply does not hyphenate the first word of a paragraph. If you need this hyphenated you have to have glue before it such as \hspace{0pt}. This (mis)-feature is shared with tex variants such as ptex and xetex, however luatex does include the first word in its hyphenation pass, and so would hyphenate your example without the extra space.

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