CSS Writing Modes Level 4 defines CSS support for various writing modes and their combinations, including left-to-right and right-to-left text ordering as well as horizontal and vertical orientations.
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1. Introduction to Writing Modes
CSS Writing Modes Level 4 defines CSS features to support for various international
writing modes, such as left-to-right (e.g. Latin or Indic), right-to-left
(e.g. Hebrew or Arabic), bidirectional (e.g. mixed Latin and Arabic) and
vertical (e.g. Asian scripts).
The inline base direction is the primary direction in which
content is ordered on a line and defines on which sides the “start”
and “end” of a line are. The direction property specifies the
inline base direction of a box and, together with the unicode-bidi property and the inherent directionality of any text content, determines
the ordering of inline-level content within a line.
The block flow direction is the direction in which
block-level boxes stack and the direction in which line boxes stack
within a block container. The writing-mode property determines the
block flow direction.
The typographic mode determines if text should apply
typographic conventions specific to vertical flow for vertical
scripts.
This concept distinguishes vertical flow for vertical scripts from
rotated horizontal flow.
A horizontal writing mode is one with horizontal lines of
text, i.e. a downward or upward block flow.
A vertical writing mode is one with vertical lines of text,
i.e. a leftward or rightward block flow.
These terms should not be confused with vertical block flow (which is a downward or
upward block flow) and horizontal block flow (which is
leftward or rightward block flow). To avoid confusion, CSS
specifications avoid this latter set of terms.
Writing systems typically have one or two native writing modes. Some
examples are:
Latin-based systems are typically written using a left-to-right inline
direction with a downward (top-to-bottom) block flow direction.
Arabic-based systems are typically written using a right-to-left
inline direction with a downward (top-to-bottom) block flow direction.
