This proposal explores a way to turn Zero Width Spaces into visible spaces.
The driving use case is support for optional spacing in Japanese (known as “分かち書き”)
for the benefit of language learners and people with dyslexia.
If adopted, this proposal is expected to be incorporated into [CSS-TEXT-3] or [CSS-TEXT-4].
CSS is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, etc.
Please send feedback
by filing issues in GitHub (preferred),
including the spec code “css-space-expansion” in the title, like this:
“[css-space-expansion] …summary of comment…”.
All issues and comments are archived.
Alternately, feedback can be sent to the (archived) public mailing list firstname.lastname@example.org.
In a number of languages and writing system, such as Japanese or Thai,
words are not deliminated by spaces (or any other character)
as is the case in English (See Approaches to line breaking for a discussion the approach various languages take to word separation and line breaking).
However, even if text without spaces is the dominant style in such languages,
there are cases where making word boundaries (or phrase boundaries) visible through the use of spaces
This is a purely stylistic effect, with no implication on the semantics of the text.
In Japan for instance, this is commonly done in books for people learning the language—young children or foreign students.
People with dyslexia also tend to find this style easier to read.
Recent pushes by the Japanese government
for electronic text-books have raised the demand for this type of features,
and proprietary ebook solutions are being proposed.
The mechanism proposed in this specification builds upon the existing use
of the wbr element
or of U+200B ZERO WIDTH SPACE
in the document markup as a word (or phrase) delimiter.
While this practice is not that common,
it is a semantically valid use of that unicode character,
and the ability to trigger stylistic effects based on it
can only encourage its use.
Should we allow more freeform values, like <string>, possibly limited to 1 character?
This property enables all instances of U+200B ZERO WIDTH SPACE to be replaced by the specified character.
Instances of wbr are considered equivalent to U+200B, and are also replaced.
This substitution happens before layout, so all layout operations that depend on the characters in the content (such as CSS Text 3 § 4.1 The White Space Processing Rules, line breaking, or intrinsic sizing) must use that character instead of the original U+200B.
This property has no effect.
All instances of U+200B ZERO WIDTH SPACE are replaced by U+0020 SPACE.
All instances of U+200B ZERO WIDTH SPACE are replaced by U+3000 IDEOGRAPHIC SPACE.
Like text-transform, this property transforms text for styling purposes.
It has no effect on the underlying content,
and must not affect the content of a plain text copy & paste operation.
This almost looks like instead of a new property,
we could just add two new values of the text-transform property.
Using this, it is possible not only to enable the rather common phrase based spacing,
but also word by word spacing that is likely to be preferred by people with dyslexia to reduce ambiguities,
or other variants such as a combination of phrase-based spacing and of word-based wrapping.
Security and Privacy Considerations
This appendix is non-normative.
There are no known security or privacy impacts of this feature.
Does this specification deal with personally-identifiable information?
Does this specification deal with high-value data?
Does this specification introduce new state for an origin that persists across browsing sessions?
Does this specification expose any other data to an origin that it doesn’t currently have access to?
Does this specification enable new script execution/loading mechanisms?
Does this specification allow an origin access to a user’s location?
Does this specification allow an origin access to sensors on a user’s device?
Does this specification allow an origin access to aspects of a user’s local computing environment?
Does this specification allow an origin access to other devices?
Does this specification allow an origin some measure of control over a user agent’s native UI?
Does this specification expose temporary identifiers to the web?
Does this specification distinguish between behavior in first-party and third-party contexts?
How should this specification work in the context of a user agent’s "incognito" mode?
No difference in behavior is expected or needed.
Does this specification persist data to a user’s local device?
Does this specification have a "Security Considerations" and "Privacy Considerations" section?
Yes, this is the role of this Appendix.
Does this specification allow downgrading default security characteristics?
Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words “MUST”,
“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. [RFC2119]
Examples in this specification are introduced with the words “for example”
or are set apart from the normative text with class="example",
This is an example of an informative example.
Informative notes begin with the word “Note” and are set apart from the
normative text with class="note", like this:
Note, this is an informative note.
Advisements are normative sections styled to evoke special attention and are
set apart from other normative text with <strong class="advisement">, like
this: UAs MUST provide an accessible alternative.
Conformance to this specification
is defined for three conformance classes:
A style sheet is conformant to this specification
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module.
A renderer is conformant to this specification
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by this specification by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.)
An authoring tool is conformant to this specification
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module.
So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers must treat as invalid (and ignore
as appropriate) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents must not selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
Implementations of Unstable and Proprietary Features
Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec.
To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS