[Tex/LaTex] Effect of changing \fontfamily and \familydefault

fonts

Assume I would like to change the font for a section of text, e.g. use Bookman for both headings and paragraphs (similarly to the explanations in this community wiki guide).

If I change the \familydefault, as in section (1), only headings are affected. If on the other hand I select Bookman as the \fontfamily, it affects only paragraph text but not headings (2). Combining both commands gives the desired result (3), as does adding a \normalfont command to \familydefault* (4).

What causes this behaviour? Does \fontfamily set some "currentfont" variable which is not accessed when headings are formatted? And why does changing \familydefault immediately affect headings, but not text?

 

*This was pointed out in a comment by @mpg.

enter image description here

\documentclass{article}
\usepackage[T1]{fontenc}

%print a _short section of lipsum text
\newcommand{\shlipsum}{%
    \section{A quick brown fox}
    Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, adipiscing vitae, felis. Curabitur dictum gravida mauris. Nam arcu libero, nonummy eget, consectetuer id, vulputate a, magna.\\%
}

%reset font to typewriter CM
\newcommand{\resetfont}{\renewcommand{\familydefault}{cmtt}\normalfont}

\begin{document}

\resetfont
\renewcommand{\familydefault}{pbk}  %sets heading only
\shlipsum

\resetfont
\fontfamily{pbk}\selectfont         %sets paragraph text only
\shlipsum

\resetfont
\renewcommand{\familydefault}{pbk}
\fontfamily{pbk}\selectfont
\shlipsum

\resetfont
\renewcommand{\familydefault}{pbk}
\normalfont
\shlipsum

\end{document}

Best Answer

\fontfamily{pbk}\selectfont selects that family from that point for the rest of the current group.

\renewcommand{\familydefault}{pbk} Just redefines that macro and does nothing unless something does \fontfamily{\familydefault}\selectfont. That combination isn't normally done explicitly but is part of \resetfont or \normalfont which heading commands usually use so that they get consistent fonts even if the text at that point in the document is locally using a different font style.

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