on a somewhat related topic, I have noticed that Sigil 0.6.2 release validates CSS against CSS level 3, whereas the latest git build validates against 2.1, and as far as I can understand it, the epub 2.0.1 specification
is based on CSS 2.0:
1.3.5: Relationship to CSS
This specification defines a style language based on CSS 2. (Note that the CSS 2.1 specification is currently still at "Working Draft" status.) The style sheet MIME type text/x-oeb1-css has been deprecated in favor of text/css.
The CSS-based style sheet constructs in this specification define required rendering functionality. To minimize the burden on Reading System developers and device manufacturers, not all CSS 2 properties are included. A few additional properties and values have been added to support page layout, headers, and footers. These, taken together, constitute the OPS CSS 2.0 required subset.
In a number of cases, this specification does not require Reading Systems to provide the full range of rendering that a standard CSS style sheet might request. For example, some Reading Systems will use monochrome displays. It would neither be acceptable to limit all Reading Systems to monochrome, nor to declare color use a non-standardized extension beyond OPS. In such cases, the CSS settings are allowed, and keep their meanings; but a conforming Reading System may gracefully degrade to a simpler rendering.
A conforming Reading System must render all OPS CSS 2.0 required subset properties. A Reading System may support CSS properties beyond the OPS CSS 2.0 required subset, however, any unsupported properties must be gracefully degraded per the CSS 2.0 specification.
It is of interest that validation against 2.1 throws errors that are not present in 2.0 or 3.0, yet the CSS is accepted by ADE (which I consider my harshest critic).
Just wondering what the rationale is for the choices / changes?
Albert (who apologizes for the attempted thread hijack)