Microtypography and the -bag properties

The engine exposes a handful of controls that plain CSS does not know. They all carry the -bag- prefix, cascade and inherit like normal properties, and are safe to leave in stylesheets that are also used in browsers (unknown properties are ignored there).

Font expansion

Justification usually has only the word spaces to work with. Font expansion (the hz-program idea) additionally lets the glyphs themselves stretch or shrink by a small percentage, which evens out word spacing and helps the line breaker find better breaks. It is on by default at 5%; the percentage is the maximum change of a glyph’s width:

body { -bag-font-expansion: 0%; }   /* switch it off */
body { -bag-font-expansion: 2%; }   /* more conservative than the default */

At sane values (2 to 5 percent) the distortion is invisible at reading distance; what remains visible is the calmer word spacing.

Line breaker tuning

Two knobs steer the paragraph breaker directly:

blockquote { -bag-linebreak-tolerance: 8; }
th         { -bag-linebreak-hyphen-penalty: 200; }

• -bag-linebreak-tolerance (default 4) is the badness a line may reach before the breaker refuses it. Raise it for very narrow measures (table cells, margin columns) where the default finds no acceptable break and lines come out overfull; the price is looser word spacing.
• -bag-linebreak-hyphen-penalty makes hyphenated line ends more expensive. Raise it to hyphenate less without forbidding hyphenation outright (hyphens: none does that); it is the gentler tool because emergencies can still hyphenate.

Reference: all -bag properties