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List:       xml-dev
Subject:    Re: [xml-dev] Many different syntaxes in XML - is that good language design?
From:       Pete Cordell <pete++xmldev () codalogic ! com>
Date:       2022-03-07 15:52:46
Message-ID: 6bacc2f4-51c3-29df-ceef-3829ce57be68 () codalogic ! com
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On 07/03/2022 14:20, Norman Gray wrote:
> As Peter mentioned, those aren't different 'syntaxes'.  There's just one syntax \
> being described here -- the document syntax -- which has a relatively small number \
> of lexical elements.  Thus 'the syntax' is the set of rules about how all of those \
> lexical elements may be combined.  And as Shaun mentions, XML is remarkable for \
> being an embedded syntax (embedded within the flow of document text, that is), \
> which has only two characters which shift to 'markup' (TeX, which is doing the same \
> thing in a way, has 16 different categories of character). 
> A possibly interesting tangent: there are fewer lexical elements here than might be \
> obvious, depending on your point of view.  One of these is '<!', which is what SGML \
> described as 'markup declaration open', meaning a bit of markup that isn't an \
> element, but is instead somewhat 'meta'.  The following 'markup declaration' could \
> be 'DOCTYPE' or '[CDATA[' (and a couple more).  Entertainingly, it could also be \
> empty: '<!>', though that empty markup declaration could contain commented text: \
> the comment characters in SGML were '--' as open and close characters, which could \
> appear anywhere; thus you could, I recall have

I'm surprised I hadn't spotted this before!!!  So in essence:

- "<" means escape from text flow

- If "<" is followed by a "!" it is a standard defined "meta" data item 
/ directive.

- If "<" is followed by "?" it is user defined meta data / directive.

- If "<" is followed by a letter then it is user defined text markup.

&??? allows you to include "<" in text and insert an actual "&".

Viewed like that it seems a fairly minimal and efficient syntax.

(It does make me wonder why the CDATA section 'directive' wasn't just 
<!CDATA[...]>.  Even more curious, given all the SGML things that got 
dropped, is how it got included in XML.  It creates just as many 
problems as it solves.)

Cheers,

Pete.
-- 
---------------------------------------------------------------------
Pete Cordell
Codalogic Ltd
Read & write XML in C++, http://www.xml2cpp.com
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