Insert an italic correction, a small space defined by the font
designer for each character (possibly zero), to avoid the character
colliding with whatever follows. When you use
takes the correction from the font metric file, scales it by any
scaling that has been applied to the font, and then inserts that much
Here, were it not for the
\/, the before-character
italic f would hit the after-character roman H
because the italic letter f leans far to the right.
If after-character is a period or comma then don’t insert an italic correction since those punctuation symbols are so low to the baseline already. However, with semicolons or colons, as well as with normal letters, the italic correction can help. It is typically used between a switch from italic or slanted fonts to an upright font.
When you use commands such as
\textsl to change fonts, LaTeX automatically inserts the
italic correction when needed (see Font styles). However,
declarations such as
\slshape do not automatically insert italic corrections.
Upright characters can also have an italic correction. An example
where this is needed is the name
pdf\/\TeX. However, most
upright characters have a zero italic correction. Some font creators
do not include italic correction values even for italic fonts.
Technically, LaTeX uses another font-specific value, the so-called
slant parameter (namely
\fontdimen1), to determine whether to
possibly insert an italic correction, rather than tying the action to
particular font commands.
There is no concept of italic correction in math mode; math spacing is done in a different way.