[OS X TeX] Why is cmr10.tfm not being used?

[Doug McKenna]

Herbert Schulz wrote -

>First cmr10.tfm is NOT a font, just use cmr10.

Sorry for the confusion.  It is called the /font command, not the 
\fontmetric command, so one tends to think one is specifying a font, 
re-inforced when the tracing mechanism uses the phrase "select font" to 
tell you what you thought you were doing.

Yes, it's just a metric file whose name is used by TeX to connote the 
current font's measurements.

>Second, why would you expect a pdf file to be produced when there is 
>nothing in the file. Try

Again, apologies for not explaining myself less succinctly.

I'm not interested in whether a PDF file is produced, so I created a 
Minimum Working Example for my question, which doesn't require any PDF 
file to be produced.  If I insert "Hello, world!" as the text, and 
include the %%!TEX commments you suggested, the log file has the same 
trace in it (marked with an arrow below):

This is pdfTeX, Version 3.1415926-1.40.11 (TeX Live 2010) (format=pdftex 
2011.2.17)  7 SEP 2012 21:12
entering extended mode
 \write18 enabled.
 file:line:error style messages enabled.
 %&-line parsing enabled.
**FontTest.tex
(./FontTest.tex{into \tracingassigns=1}
{changing \tracingonline=0}
{into \tracingonline=1}
{changing \fontname=\fontname}
{into \fontname=select font nullfont}       <---
{reassigning current font=\fontname}
{globally changing \outputpenalty=0}
{into \outputpenalty=-20000}
{changing \boxmaxdepth=16383.99998pt}
{into \boxmaxdepth=4.0pt}
{reassigning \dimen0=0.0pt}
{changing \baselineskip=12.0pt}
{into \baselineskip=24.0pt}
{reassigning \lineskiplimit=0.0pt}
{reassigning current font=\fontname}
[1{/usr/local/texlive/2010/texmf-var/fonts/map/pdftex/updmap/pdftex.map}]{g
loba
lly changing \count0=1}
{into \count0=2}
 
)</usr/local/texlive/2010/texmf-dist/fonts/type1/public/amsfonts/cm/cmr10.p
fb>

Output written on FontTest.pdf (1 page, 12033 bytes).
PDF statistics:
 12 PDF objects out of 1000 (max. 8388607)
 7 compressed objects within 1 object stream
 0 named destinations out of 1000 (max. 500000)
 1 words of extra memory for PDF output out of 10000 (max. 10000000)

The question is, why is the trace of the execution saying

{changing \fontname=\fontname}
{into \fontname=select font nullfont}
{reassigning current font=\fontname}

up near the top, when I thought I was selecting cmr10?

I'm just trying to get my mental model of what TeX does in order.

Thanks, but still wondering.  Perhaps I should ask on the usual texhax 
list, but I started here because I thought it might be a misplaced file 
on the Mac problem.

Doug McKenna