xml-dev - Re: FW: "+" and "?" used with "|" and "*" in the DTD

[Lars Marius Garshol <larsga@garshol.priv.no>]

* Dylan Walsh
|
| The following is from the RSS 0.91 DTD
| (http://my.netscape.com/publish/formats/rss-0.91.dtd). I was shown this
| DTD
| by a colleague who was asking a different question, but the following line
| stuck out:
| 
| <!ELEMENT channel (title | description | link | language | item+ | rating?
| | image? | textinput? | copyright? | pubDate? | lastBuildDate? | docs?
| | managingEditor? | webMaster? | skipHours? | skipDays?)*>
| 
| Isn't it correct to say that the plus and the question marks are
| redundant?

Yes, it is.

The problem is that XML DTDs are not really strong enough to express
the true structure of the application, and so these redundant
modifiers were put in to provide extra information to human readers.

SGML DTDs have an additional separator '&', which means include each
content particle once in any order. If you replace each '|' with a '&'
(and remove the final '*') you get the true intent behind the content
model.

--Lars M.