CSS4 Values and Units, 6.1.1. Font-relative lengths section, ic unit https://www.w3.org/TR/css-values-4/#ic states " ic unit Equal to the used advance measure of the “水” (CJK water ideograph, U+6C34) glyph found in the font used to render it. This measurement is a typically an exact measure (in the few fonts with proportional fullwidth glyphs, an approximation) of a **single fullwidth glyph’s advance measure**, thus allowing measurements based on an expected glyph count. In the cases where it is impossible or impractical to determine the ideographic advance measure, it must be assumed to be 1em. " 9 Tests ------- In horizontal-tb writing-mode: http://w3c-test.org/css/css-values/ic-unit-001.html With text-orientation: upright; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-002.html With text-orientation: mixed; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-003.html With text-orientation: sideways; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-004.html In horizontal-tb writing-mode: http://w3c-test.org/css/css-values/ic-unit-008.html With (initial) text-orientation: mixed; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-009.html With text-orientation: mixed; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-010.html With text-orientation: upright; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-011.html With text-orientation: sideways; and writing-mode: vertical-rl; http://w3c-test.org/css/css-values/ic-unit-012.html Right now, no browser supports any of these 9 tests https://wpt.fyi/results/css/css-values?label=master I searched for duplicate and did not find any.
Correspondent Mozilla Bug report https://bugzilla.mozilla.org/show_bug.cgi?id=1531223
<rdar://problem/48532261>
+1 to this request. This should happen.
Correspondent Blink Bug report https://bugs.chromium.org/p/chromium/issues/detail?id=937101
Resolved in https://bugs.webkit.org/show_bug.cgi?id=204276