Font grid restrictions for LaTeX

[topological-modular-forms]

As noted by Robert Allgeyer:

If you are designing with cubic splines (OpenType with PostScript outlines, not TrueType with quadratic splines) and your font grid is 1000 units per em (standard for OpenType):

A "well behaved" font has its tallest text character no taller than 840 grid units above baseline, and its deepest text character no deeper than 260 grid units below baseline. Characters used in math expressions and diagrams (not running text) do not need to comply. For running text, in Latin-1 plus curly quotes and similar typography, the tallest character will be an uppercase letter with diacritical mark, and the deepest letter will be among gjpqy. But beware, if you also use slashes or bars in text. Also beware if you use superscripts (such as footnote markers) that are in raised boxes, instead of called directly from the font as OpenType features.

Reason: The LaTeX \strut is 0.7\baselineskip above baseline, and 0.3\baselineskip below baseline. Some (non-TeX) programs use a default, tight line spacing of 1.2em. If you choose this, then a "well-behaved" font will fit within the strut at tight line spacing, leaving 0.1em gap between lines.

Many ordinary text fonts, used for book publishing (to paper), are "well-behaved". Some, not all, LaTeX fonts are "well-behaved, or nearly so. A few fonts (such as fbb) are far from "well-behaved", and can cause line spacing issues if not used carefully.