ISSUE-40: Should the <length> <length> offset be optional in a shadow?

box-shadow grammar

Should the <length> <length> offset be optional in a shadow?

CSS3 Backgrounds and Borders
Raised by:
Bert Bos
Opened on:
See also thread at

1) [Minor:] the grammar contains two errors: it requires at least two shadows instead of one; and it makes the comma optional. The best fix depends on the answer to the next question.

2) The offset (<length> <length>) is optional and defaults to '0 0', which means that an omitted offset makes the shadow invisible and is thus almost never useful. There are at least two solutions: require an offset or make the default more useful.

The similar 'text-shadow' property ( makes the offset required. Whatever solution is chosen, 'box-shadow' and 'text-shadow' should probably have the same syntax.

* Solution 1, don't omit the offset:

none | <shadow> [ , <shadow> ]*

where <shadow> is

<length> <length> <length>? <color>? |
<color> <length> <length> <length>?

* Solution 2, better default offset:

An omitted offset could default to '1px 1px' or to a value chosen by the UA.
Related Actions Items:
No related actions
Related emails:
  1. [Publish] [css-position] Publish CSS Positioned Layout Working Draft (from on 2015-01-12)
  2. [css3-background] Issues and Proposed Resolutions (from on 2008-05-13)
  3. ISSUE-40 (box-shadow grammar): Should the <length> <length> offset be optional in a shadow? [CSS3 Backgrounds and Borders] (from on 2008-05-07)

Related notes:

non-zero default offsets rejected: nobody likes this idea and it's inconsistent with text-shadow

Elika Etemad, 12 May 2008, 21:12:50

making optional offsets rejected, issue open for grammar errors fix

Elika Etemad, 12 May 2008, 21:19:57

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Peter Linss <>, Daniel Glazman <>, Alan Stearns <>, Rossen Atanassov <>, Chairs, Chris Lilley <>, Bert Bos <>, Staff Contacts
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