CSS-008 on an empty declaration in a stylesheet — issue #238 was fixed for style attributes only #1680

A stray semicolon in a declaration block is reported as a parse error when it
appears in a stylesheet, but not when it appears in a style attribute.

ERROR(CSS-008): EPUB/s.css(1,9): An error occurred while parsing the CSS:
Token ";" not allowed here, expecting a property name.

This was already accepted and fixed, for one path

#238 (2013) reports the same
message with the same reasoning — that CSS's declaration production matches
empty, so a declaration list may begin with ;. It was marked Accepted and
closed as Fixed by r450.

That fix is still working. Against 5.3.0, in a style attribute:

So the attribute path is still parsed and still reports genuinely malformed
values — it simply tolerates the empty declaration, correctly. The stylesheet
path does not:

a:link {;color: #000000}     /* CSS-008 at 1,9  */
a:link {color: #000;;}       /* CSS-008 at 1,21 */

Why the tolerant behaviour is the right one

CSS Syntax Level 3 discards the token explicitly. In both 5.4.4 Consume a
style block's contents and 5.4.5 Consume a list of declarations, the step for
<semicolon-token> is:

Do nothing.

CSS 2.1's core grammar (Appendix G) makes each declaration slot optional:

ruleset
  : selector [ ',' S* selector ]*
    '{' S* declaration? [ ';' S* declaration? ]* '}' S*
  ;

Impact

CSS-008 is an ERROR, so it changes the verdict: a publication that is otherwise
completely clean fails the check because of a character that has no effect on
rendering. It occurs in the wild — the case that prompted this is a
commercially distributed EPUB whose stylesheet contains
a:link {;color: #000000;text-decoration: none;} and which is otherwise clean.

Reproduction

A minimal EPUB 3 whose only stylesheet is a:link {;color: #000000} reports
0 fatals / 1 error. Removing the single ; and changing nothing else reports
No errors or warnings detected.

Where it comes from

CSSHandler.error() turns any exception from the CSS parser into CSS-008
unconditionally, so this surfaces the tokenizer's strictness rather than a rule
the checker decided on. Consistent with that, no CSS-008 scenario in
content-document-css.feature covers this shape — content-css-syntax-error
is about unterminated blocks, which really are malformed.