xml-dev - Re: (off-topic) Re: Recursive Children?

[Joe English <jenglish@flightlab.com>]

Rick JELLIFFE <ricko@geotempo.com> wrote:

> > > Does anyone know if (and how) I can have one element contain itself?
>
> In SGML you could, potentially.  (I hope ISO 8879 said this is an error :-)
> Given the declaration
>  <!ATTLIST x
>      id ID #IMPLIED
>      refid IDREF #CONREF >
> you could attempt
>  <x  id="x1"  refid="x1" >
>
> where #CONREF means "if this attribute is used, the contents of the
> element being pointed to can be taken as the contents of this element
> (which cannot have any contents if #CONREF is specified)".

Actually no: '#CONREF' *only* means that "if this attribute
is specified, the element to which it belongs must be empty".

The intended semantics is that the application could generate
content for the element (in some unspecified way), but the parser
doesn't do anything else with #CONREF attributes.

> That allowed
> SGML to specify many-to-one relationships on "children", but it wasn't
> used much because most SGML was stream-processed.

Attributes with declared value REFID turn into an 'irefnode'
property in the grove, not a 'subnode' property; and the
presense of an attribute with a #CONREF default value
only ensures that the parent node will have _no_ 'subnode'
property (or an empty one, I'm not sure which, but it
amounts to the same thing).  So the "children" relation
always forms a tree, not a DAG or cyclic graph.


--Joe English

  jenglish@flightlab.com