Question

There seems to be a breaking (i.e. backwards-incompatible) change in the CSS Syntax Module Level 3 specification upcoming draft: trailing semicolon after the last declaration in a block is now perhaps required.

Compare the old wording (W3C Working Draft 13 August 2003):

4.8. Rule sets, declaration blocks, and selectors
A declaration-block (also called a {}-block in the following text) starts with a left curly brace ({) and ends with the matching right curly brace (}). In between there must be a list of zero or more semicolon-separated (;) declarations.

with the new one (Editor’s Draft 14 June 2012):

2. Description of CSS’s Syntax
A rule starts with a selector (defined by the Selectors specification), then has a {}-wrapped block containing a sequence of declarations. The selector specifies which elements the declarations will apply to. Each declaration has a property name, followed by a colon and the property value, and finished with a semicolon.

(emphasis mine).

So that nifty short forms, e.g.:

em { color: lime }

(this is currently given as valid example in the CSS Color Module Level 3 recommendation) will no longer validate.

Could someone more knowledgeable about the whole Level 3 drafts collection please verify? To future-proof stylesheets, do we really have to overhaul existing CSS files (and insert semicolons if missing) before the specification gets finalized or did I misunderstand something?

Answer 1

Looks like there currently is an ambiguity in the spec.

You correctly pointed out that 2. Syntax Description section prescribes ending every rule with a semicolon:

Each declaration has a property name, followed by a colon and the property value, and finished with a semicolon.

And at the same time, description of the parsing automaton in section 3.6.8. Declaration-value mode reads that a closing brace without a semicolon correctly ends a declaration and current rule at the same time:

} token

Append the current declaration to the value of the current rule. Pop the current rule from the stack of open rules, and append it to the value of the new current rule. Switch to the current rule’s content mode.

So according to 3.6.8 trailing semicolon is optional.

I can’t say about actual intention of the specification authors. But current situation should probably be reported and fixed. Most certainly they don’t have intention of breaking the compatibility with CSS 2.1 and will reword their Syntax Description section in the final version.