Re: CSS selectors are syntactic sugar for XPath expressions

I, um, don't think you've met many CSS developers?  Selectors came 
first, and there are definitely selectors without XPath equivalents.

There's a Venn diagram with a big overlap, but wow the separations are 
important.  I don't think that what you want to do with CSS is in the 
overlap zone.

Thanks,
Simon


On 3/21/2022 1:58 PM, Roger L Costello wrote:
> Hi Folks,
>
> Recall that CSS rules consist of two parts: a selector and styling statements. For example, this rule says the content of the <h1> element is to be italicized:
>
> h1 { font-style: italic; }
>
> Multiple elements can be identified in a rule by separating their names with commas, e.g.,
>
> h1, h2, h3  { font-style: italic; }
>
> That is equivalent to these three rules:
>
> h1 { font-style: italic; }
> h2 { font-style: italic; }
> h3 { font-style: italic; }
>
> Both forms say this: Italicize the content of h1 headers; italicize the content of h2 headers; and italicize the content of h3 headers. The styling actions on h1, h2, and h3 are independent of one another.
>
> The CSS selectors are syntactic sugar (convenient shorthand notations) for equivalent XPath expressions. For example:
>
> div  		//div
> h1 em  		//h1//em
> .title   		//*[@class='title']
> #mars    	//*[@id='mars']
> div#mars 	//div[@id='mars']
>
> CSS selectors are really nice. They are simple and powerful.
>
> I would like to use the "CSS approach" for a language that I am creating. But there is a problem. Suppose the language that I am creating is to operate on this XML:
>
> <person>
>    <name>John Doe</name>
>    <telephone>555-123-4567</telephone>
>    <latitude>42.366978</latitude>
>    <longitude>-71.022362</longitude>
> </person>
>
> The latitude/longitude pair corresponds to the location of Logan airport in Boston. So the XML document shows John Doe at Logan airport. I would like a rule that fuzzes the latitude and longitude elements so that you only know John Doe's location to within a 10 kilometer radius of Boston. One might imagine a rule like this:
>
> latitude, longitude { fuzz_location(...); }
>
> However, the semantics of CSS says that that rule is equivalent to two independent rules:
>
> latitude		{ fuzz_location(...); }
> longitude 	{ fuzz_location(...); }
>
> That's not what I want. The latitude and longitude values are intertwined; their values must be operated on together, not independently.
>
> I want to avoid using the XPath syntax for selectors, as XPath is too complex for my users.
>
> I want to use the simple CSS syntax, but somehow I need to extend its semantics so that a rule can select a set of elements that are operated on together. Have you done this type of thing -- extended the CSS semantics so that a selected set of elements are operated on together?
>
> /Roger
>
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