Guide to LaTeX (4th Edition) (Tools and Techniques

92 Chapter 4. Displayed Text
The parameters lift, width, and height are all lengths (Section 2.4.1). If
lift has a negative value, the rectangle is set below the baseline.
It is also possible to have a rule box of zero width. This creates an
invisible line with the given height. Such a construction is called a strut
and is used to force a horizontal box to have a desired height or depth
that is different from that of its contents. For this purpose, \vspace is
inappropriate because it adds additional vertical space to that which is
already there.
For example: \fbox{Text} produces Text . In order to print Text ,
one has to tell T E X that the box contents extend above and below the
baseline by the desired amounts. This was done with \fbox{\rule[-2mm]
{0cm}{6mm}Text}. What this says is that the text to be framed consists
of ‘an invisible bar beginning 2 mm below the baseline, 6 mm long,
followed by the word Text’. The vertical bar indeed remains unseen, but
it determines the upper and lower edges of the frame.
4.7.7 Nested boxes
The box commands described above may be nested to any desired level.
Including an LR box within a parbox or a minipage causes no obvious
conceptual difficulties. The opposite, a parbox within an LR box, is also
possible, and is easy to visualize if one keeps in mind that every box is a
unit, treated by L AT E X as a single character of the corresponding size.
A parbox inside an \fbox command has the effect that the
entire parbox is framed. The present structure was made with
\fbox{\fbox{\parbox{10cm}{A parbox...}}}
This is a parbox of width 10 cm inside a framebox inside a
second framebox, which thus produces the double framing
effect.
Enclosing a parbox inside a \raisebox allows vertical
displacements of any desired amount. The two boxes
here both have positioning [b], but the one at the right
has been produced with:
\raisebox{1cm}{\begin{minipage}[b]{2.5cm}
a b c d e ... x y z\\
\underline{baseline}
\end{minipage} }
a b c d e f g h i
j k l m n o p q r
s t u v w x y z
baseline
which displaces it upwards by 1 cm. baseline
A very useful structure is one in which minipage environments are
positioned relative to one another inside an enclosing minipage. The
positioning argument of the outside minipage can be used to align its