\baselineskip per paragraphThe \baselineskip is not (as one might hope) a property of a
line, but of a paragraph. As a result, in a 10pt (nominal)
document (with a default \baselineskip of 12pt), a
single character with a larger size, as:
{\Huge A}
will be squashed into the paragraph: TeX will make sure it doesn't
scrape up against the line above, but won't give it "room to
breathe", as it does the text at standard size; that is, its size
(24.88pt) is taken account of, but its \baselineskip
(30pt) isn't. Similarly
Paragraph text ...
{\footnotesize Extended interjection ...
... into the paragraph.}
... paragraph continues ...
will look silly, since the 8pt interjection will end up set
on the 12pt \baselineskip of the paragraph, rather than
its preferred 8.5pt. Finally, something like
Paragraph text ...
... paragraph body ends.
{\footnotesize Short comment on paragraph.}
Next paragraph starts...
will set the body of the first paragraph on the constricted
\baselineskip of the \footnotesize comment.
So, how to deal with these problems? The oversized (short) section is
typically corrected by a strut: this word comes from movable
metal typography, and refers to a spacer that held the boxes (that
contained the metal character shapes) apart. Every time you change
font size, LaTeX redefines the command \strut to provide the
equivalent of a metal-type strut for the size chosen. So for the
example above, we would type
Paragraph text ...
{\Huge A\strut}
... paragraph continues ...
However, more extended insertions (whether of larger or smaller text)
are always going to cause problems; while you can strut larger text,
ensuring that you strut every line will be tiresome, and there's no
such thing as a "negative strut" that pulls the lines together for
smaller text.
The only satisfactory way to deal with an extended insertion at a
different size is to set it off as a separate paragraph. A
satisfactory route to achieving this is the quote
environment, which sets its text modestly inset from the enclosing
paragraph:
Paragraph text ...
\begin{quote}
\footnotesize This is an inset account
of something relevant to the enclosing
paragraph...
\end{quote}
... paragraph continues ...
Such quote-bracketing also deals with the problem of a trailing
comment on the paragraph.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=baselinepar