[css-page-3] Replace CSS 2.1 syntax definitions by CSS syntax

[SebastianZ]

The minutes from 2016-10-12 resolved on removing the CSS grammar section from CSS 2.2 and instead refer to the CSS Syntax module. Though the CSS Paged Media Module still uses that grammar for the definition of the @page rule.

This syntax should be replaced by something like this*:

@page <page-selector-list> { <page-body> }

where
<page-selector-list> = [ <page-selector># ]?
<page-body> = <declaration>? [ ; <page-body> ]? | <page-margin-box> <page-body>
<page-selector> = <pseudo-page>+ | <ident> <pseudo-page>*
<page-margin-box> = <page-margin-box-type> { <declaration-list> }
<pseudo-page> = : [ left | right | first | blank ]
<page-margin-box-type> = @top-left-corner | @top-left | @top-center | @top-right | @top-right-corner | @bottom-left-corner | @bottom-left | @bottom-center | @bottom-right | @bottom-right-corner | @left-top | @left-middle | @left-bottom | @right-top | @right-middle | @right-bottom

Sebastian

* For reference, I used that syntax definition for @page on MDN.

[SebastianZ]

The previous syntax definition got replaced by one following the Syntax spec. in 30e1273.

This change let parts still be defined in prose. @tabatkins As you made the change, would you agree to define everything in the formal syntax as I did back then?

Sebastian

[tabatkins]

I'm not sure I understand your question. The only difference between the grammar you suggested in the OP and what I eventually committed is that I used the guidelines in the Syntax spec for defining rules (which requires prose to specify what's allowed in a given <definition-list>), while your grammar tries to enforce the prose more strictly in the grammar itself. I intentionally wrote the Syntax guidelines to not do that, precisely because writing a correct and understandable grammar for block contents in various situations is difficult.

[SebastianZ]

Fair enough.

Sebastian