Typesetting glue ($(g,s,t)$)

Typesetting glue represents adjustable space between pieces of typeset material. In a finite, single-order model, describe a glue item by a nominal width $g_i$, stretch coefficient $s_i\ge 0$ and shrink coefficient $t_i\ge 0$. A shared line adjustment ratio $r$ givesThus a negative $r$ reduces the gap. The coefficients describe relative flexibility; they need not be identical for all spaces. This model is a useful part of text justification.^[ref]

For example, two nominal gaps of width 3 with stretch coefficients 1 and 3 become $3.5$ and $4.5$ when $r=1/2$. Their total extra width is 2. With shrink coefficients 1 and 1, $r=-1$ makes both gaps width 2. The same natural line can therefore reach different targets by using the appropriate coefficients.

TeX also distinguishes typesetting glue orders, so the finite model above does not describe every glue setting. In a horizontal line, typesetting glue changes gaps rather than stretching the outlines of the glyphs.