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[selectors4] Editorial comments on the 2013-04-17 ED

From: Simon Sapin <simon.sapin@exyr.org>
Date: Sun, 21 Apr 2013 17:04:25 +0200
Message-ID: <5173FFF9.8010000@exyr.org>
To: "www-style@w3.org" <www-style@w3.org>

Here are a few editorial comments on the Selectors 4 ED.

§3.1. should add "selector list" (as in §4.1) to the terminology.

§3.2. should mention that the subject indicator is only allowed in the 
complete profile.

§3.3 says "Some host applications may choose to scope selectors to a 
particular subtree of the document." It should also say that CSS 
stylesheets are typically not scoped, and what happens in this case. 
§7.5 already defines that :scope defaults to being equivalent to :root 
when no contextual reference element set is given, but it would help to 
remind that in §3.3.

§3.4 says "The pseudo-class concept is introduced to permit selection 
based on information that lies outside of the document tree or that 
cannot be expressed using the other simple selectors." This a bit 
misleading in the case of the 15 tree-structural pseudo-classes defined 
in this spec. The general syntax of pseudo-classes is an extension 
mechanisms: it allows adding new tests/conditions by naming them instead 
of inventing punctuation-based syntax. Only some of these tests are 
based on information that lies outside of the document tree.

Same section: "A pseudo-class always consists of a "colon" (:) followed 
by the name of the pseudo-class and, for functional pseudo-classes, by a 
value between parentheses." This seems imply that functional pseudos can 
only have one component value (as defined in Syntax and Values & Units) 
between parentheses, but really it could be any list of nested component 
values. Perhaps refer to Syntax for the concept of "a function"?

"Pseudo-class names are case-insensitive." should precise ASCII 
case-insensitive with a link to §3.6.

§3.5 should say that pseudo-elements are also ASCII case-insensitive, 
although this is implied by §3.6.

§3.6 should have an exhaustive list (and explicitly marked as such) of 
"parts that are not under the control of Selectors". If the rest of that 
paragraph is that list, just clarify that it is exhaustive.

Although almost out of scope, it could be useful to link in a note to 
the relevant section of HTML: (the existence of which I learned pretty 
late in my time implementing WeasyPrint)

"Characters in Selectors can be escaped with a backslash according to 
the same escaping rules as CSS. [CSS21]." Perhaps add a reminder that 
escaping "cancels the meaning of special characters". For example, 
#foo~a contains a combinator, but #foo\~a does not.

§4.2 should clarify: "In the fast Selectors profile, only compound 
selectors are allowed within :matches(): combinators are not allowed." 
But comma-separated lists of compound selectors are allowed, right? 
(Same comment for :not() in §4.3)

"Default namespace declarations do not affect the subject of any 
selector within a matches-any pseudo-class unless the argument is an 
explicit universal selector or a type selector." I only understood this 
based on the examples. Suggested rewording: "Default namespace 
declarations do not affect any implied universal selector within a 
matches-any pseudo-class."

§6.1 "[att] Represents an element with the att attribute, whatever the 
value of the attribute." I’m nitpicking, but I would add "even if that 
value is the empty string."

§6.6 Paraphrased: ".foo is the same as [class~=foo] in HTML but has 
higher specificity." Unless I missed something this is not the case: 
they have the same specificity.

Same section: "If an element has multiple class attributes, …" That 
never happens with HTML or XML, right? (The parser only keeps one.) 
Perhaps the note should say that, and §6.1 and §6.2 should have similar 

§6.7 "an CSS identifiers", shouldn’t that be "a CSS identifier"? (Remove 
on N and one S.)

"Selectors does not specify how a UA knows the ID-typed attribute of an 
element. The UA may, e.g., read a document's DTD, have the information 
hard-coded or ask the user." Just say that this is defined by the 
document language? There is already a note about XML and DTDs.

§7, §8, §10, §11 Although almost out of scope, it could be useful to 
link in a note to the relevant section of HTML: (the existence of which 
I learned pretty late in my time implementing WeasyPrint)

§7.1 ":any-link matches an element if the element would match :link or 
:visited." That’s a great example for :matches().

§7.4 Clarify that :target matches not the target on anything (such as 
links that exist in the document), but the target on of the document’s 
own URL. Note that the document language determines which element is the 
target of a given fragment identifier. The relevant HTML section is:

§9 Are time-dimensional pseudo-classes appropriates for slides, only one 
of which is shown at a time?

§9.1 "The :current pseudo-class represents the innermost element, or 
ancestor of an element, that is currently being displayed." I don’t 
understand "innermost or ancestor".

§10.2 The section has several occurrences of both "language range" and 
"language identifier". Are they the same thing? Shouldn’t only one term 
be used?

§11.2.1 Perhaps add a note: Even in HTML, input[type=checkbox]:checked 
may not be the same as input[type=checkbox][checked]: the attribute only 
determines the initial state: it is not change when the state is toggled 
eg. through user interaction.

§12.3 I read the linked section of css3-text, but I’m not sure exactly 
which characters are "subject to whitespace processing". It especially 
should not depend on the results of the cascade in general or the value 
of the 'white-space' property in particular. Is it doable to have an 
exhaustive list of characters in Selectors?

§12.4.2 "If an "n" token is provided (the first clause in the grammar)" 
N is the second clause.

"If an "n" token is not provided (the second clause in the grammar), the 
integer gives the offset, and the step defaults to 1." The handling of 
'odd' and 'even' is missing in this sentence.

§12.6 "among elements of the same type (tagname)" I’m not sure if 
tagname could be interpreted as as local name. Expanded name could be 
used instead.

§15 This section defines the specificity of a *complex selector*. In a 
selector list, each comma-separated complex selector has its own 

"ignore the universal selector." Shouldn’t that be plural? Each compound 
selectors in a complex selector can have a (possibly implied) universal 

Simon Sapin
Received on Sunday, 21 April 2013 15:04:49 UTC

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