[css-rhythm] East Asian Casual Vertical Rhythms

Author: kojiishi

css-rhythm/Overview.bs

@@ -15,6 +15,7 @@ Work Status: exploring
 Editor: Koji Ishii, Google, kojiishi@gmail.com
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
 ED: https://drafts.csswg.org/css-rhythm/
+TR: https://www.w3.org/TR/css-rhythm-1/
 Abstract: This module contains CSS features for aligning content size
   to multiple of unit size.
 </pre>
@@ -52,6 +53,44 @@ Introduction {#intro}
 		<p class="caption">Vertical rhythm kept through pictures and different size of text in a multi-column document.
 	</div>
 
+East Asian Casual Vertical Rhythms {#eastasia}
+----------------------------------------------
+
+In East Asia, a casual variant of vertical rhythm is widely used.
+
+Vertical rhythm is typically used in professional typography.
+While it improves readability,
+its spacing constraints require careful and well-thought design of spaces.
+
+The East Asian casual variant was
+originally a product of technical constraints of traditional word processors in '80s.
+But when the technical constraints were lifted in more modern technologies,
+with the help of square-like visual of ideographic characters,
+East Asian authors preferred to keep parts of the characteristics.
+
+In this variant of vertical rhythm,
+the requirement is loosened for the ease of use for non-professional authors.
+Text is still on the rhythm,
+so that the majority of ideographic characters are mostly on grid,
+but when author specifies borders, margins, or some other objects that may break the rhythm,
+the rhythm is shifted rather than forced.
+The strict vertical rhythm often surprises non-professional authors by forced jumps in such cases,
+while this variant combines rhythm on text and the ease of use for non-professional authors.
+
+This variant was very widely accepted in East Asia since the middle of '90s,
+such that most major word processors used in East Asia provided similar features
+by default.
+
+In this specification,
+when the 'line-height-step' property is used without combination of the 'block-step' property
+or the 'line-grid' property,
+it produces the similar effect as the East Asian casual vertical rhythm.
+
+For other cases of vertical rhythm,
+it is expected that
+the 'block-step' property or the 'line-grid' property are used,
+or that the 'line-height-step' property is used together with them.
+
 Adjusting Line Box Heights: the 'line-height-step' property {#line-height-step}
 ===============================================================================