[texhax] TeX Queries (2): Artificial Break

[Paul Stanley]

 > Then he adds \break after the word ``an'' so that TeX breaks the line
 > here instead of elsewhere, because TeX's default result here is not very
 > good. His remark about a tighter line comments on the use of \break, not
 > italic correction at all.
 >
 > Thank you. It seems we were at cross purposes there.  I won't ask you
 > about the "default result"; however, I get the impression that
 > without looking at the end result one wouldn't be able to make the
 > necessary comparison and decide whether or not the `\break' insertion
 > was preferable.
[snip]

With the \break, TeX makes three lines for this subparagraph, as follows:

LINE 1: you get italicized and slanted words that look better. The 
`\/' tells TeX to add an
LINE 2: ``italic correction'' to the previous letter, depending on 
that letter; this correction
LINE 3: is about four times as much for an `f' as for a `c, in a 
typical italic font.

Without the \break, i.e. with TeX left to its own devices, you get 
four lines as follows:

LINE 1: you get italicized and slanted words that look better. The 
`\/' tells TeX
LINE 2: to add an ``italic correction'' to the previous letter, 
depending on that letter; this
LINE 3: correction is about four times as much for an `f' as for a 
`c, in a typical italic
LINE 4: font.

The latter result isn't so bad, but the lines are quite stretched, 
and of course there is that fourth single-word line, smaller than the 
paragraph indentation, which is quite bad-looking.

By "stretched" do you mean the tracking space is too wide?

Interestingly, I've browsed the first fifteen chapters of the 
TeXbook, and I haven't been able to find any last line of a paragraph 
being smaller than the indentation (at least when directly followed 
by an indented paragraph). So it seems that Knuth paid much attention 
to that, and what we're discussing here might be a situation where he 
had to rely on \break to do so. (There aren't so many \break's 
elsewhere in the text.)

Is there a substitute for the visual inspection of the lines --- for 
example, a formula or some other heuristics --- in determining the 
appropriate amount of tracking in a paragraph (to ensure the glyphs 
aren't too stretched or compressed together)?

[snip]
I'll try to complement Reinhard's answer.

 > How is the declared width actually measured (i.e. where are the 
start > and end points of the declared width)?

That's up to the font designer; as Reinhard said, glyphs should 
simply be able to go along without kerning in most cases.

 > is there a declared height as well, and if so, can the declared width
 > be different at different declared heights?

No, a glyph's height is its topmost point; vertical spacing, at least 
in horizontal writing systems, deals with lines, not individual 
glyphs, so there is no use in adjusting the latter.

Could you expand a little more on vertical spacing please? I'm 
assuming it's not the same as leading, or is it?

[snip]

Finally, how, if at all, can tracking and kerning affect 
one-another?  for example, does the kerning of a pair of glyphs 
override the tracking in the line?

Many thanks,
Paul