The information which tells LaTeX exactly which font (.tfm)
files to load is contained in the <loading-info> part of a
\DeclareFontShape declaration. This part consists of one or more
<fontshape-decl>s, each of which has the following form:
The <number-or-range> denotes the size or size-range for which this entry applies.
If it contains a hyphen it is a
range: lower bound on the left (if missing, zero implied), upper bound
on the right (if missing, 
implied). For ranges, the
upper bound is not included in the range and the lower bound is.
Examples:
If more than one <size-info> entry follows without any intervening <font-info>, they all share the next <font-info>.
The <size-function>, if present, handles the use of <font-info>. If not present, the `empty' <size-function> is assumed.
All the <size-info>s are inspected in the order in which they appear
in the font shape declaration. If a <size-info> matches the
requested size, its <size-function> is executed. If \external@font
is non-empty afterwards this process stops, otherwise the next
<size-info> is inspected. (See also \DeclareSizeFunction.)
If this process does not lead to a non-empty \external@font,
LaTeX tries the nearest simple size. If the entry contains only
ranges an error is returned.