| em | Relative to the font size, i.e. 1.5em will be 50% larger than the base computed font size of its parent. (Historically, the height of the capital letter "M"). |
| ex | Heuristic to determine whether to use the x-height, a letter "x", or .5em in the current computed font size of the element. |
| cap | Height of the capital letters in the current computed font size of the element. |
| ch | Average character advance of a narrow glyph in the element's font (represented by the "0" glyph). |
| ic | Average character advance of a full width glyph in the element's font, as represented by the "水" (CJK water ideograph, U+6C34) glyph. |
| rem | Font size of the root element (default is 16px). |
| lh | Line height of the element. |
| rlh | Line height of the root element. |