Redefine \textsc for slightly large small caps

Question

In most fonts, the small caps are as tall as the x-height, but this looks weird when you want to tack an 's' onto the end of an abbreviation to make it plural (discussed in depth on typophile).

I can create a new command \textmc (for moyen caps) to do this easily:

\usepackage{scalefnt}
\newcommand{\textmc}[1]{\textsc{\scalefont{1.1}#1}}

But I'd prefer to just redefine \textsc. The approach that I was taking, however, seems to give me an infinite loop as it flips back and forth between defintions:

\newcommand{\oldtextsc}[1]{\textsc{#1}}
\renewcommand{\textsc}[1]{\oldtextsc{\scalefont{1.1}#1}}

Any advice on how to redefine a command which calls the original definition?

Answer 1

A straightforward way is to use \let to store the current definition of \textsc.

\let\oldtextsc\textsc
\renewcommand{\textsc}[1]{\oldtextsc{\scalefont{1.1}#1}}

(See Patching existing commands from the TeX FAQ for details.)

However, this can fail if \textsc happens to be in some place that gets written in the aux file (a section title, for instance), so a safer version is

\usepackage{letltxmacro}
\LetLtxMacro{\oldtextsc}{\textsc}
\renewcommand{\textsc}[1]{\oldtextsc{\scalefont{1.1}#1}}

(see the documentation of letltxmacro for more information).

The problem is that \textsc is a "robusted" command, so that LaTeX will write a special form of it in the aux file; something like \section{\textsc{a}} would result in LaTeX writing

\textsc  {\scalefont  {1.1}a}

and when interpreting it for the table of contents this would become

\oldtextsc{\scalefont{1.1}\scalefont{1.1}a}

and eventually to a scaling factor of 1.21.