Subject: Re: Core ideas behind SGML and XML
From: Erik Naggum <>
Date: 01 Oct 2002 23:59:06 +0000
Newsgroups: comp.lang.lisp
Message-ID: <>

* Rob Warnock
| Good point. And also, as Tim Bradshaw pointed out in a parallel reply
| <>, attributes are not permitted to have
| sub-structure[1], while sub-elements may.

  Well, actually, you can provide a NOTATION argument for attribute values.
  This would indicate the standard or other document specifying the syntax
  of the value, and the application would presumably know how to deal with
  this.  Also, there are actually some attribute types that require a flat
  list of whitespace-separated values in the actually attribute value.

| Do you mean that the application is allowed to merge (remapping as
| needed) IDs/IDREFs from *multiple* documents? ...or *across* multiple
| docs?

  ID and IDREF have many conflated uses.  IDREF can only refer to IDs in
  the same document instance, but with other mechanisms, you can refer to
  elements with a given ID.

| The corresponding thing in CL might be trying to reference the same
| #n=/#n# numbers across multiple occurrences of READ. Normally, that
| wouldn't be a problem (because it's not possible), but my twisted little
| brain just started wondering about how #n= & #n# might interact with
| #. in pathological cases, as in:

  I would have thought it fairly obvious that (list #.(foo #1=bar) #1#)
  must fail, and it did not appear any less obvious that (list #1=foo
  #.(foo #1#)) must fail.  However, this is wrong.  They work fine in
  Allegro CL, CLISP and CMUCL (and SBCL).  Hmm.

  However, when you call a `read´ function without a true `recursive-p´
  argument, that should mean that it establishes a new #n# context.

| +---------------
| | Grasping that this can be used for circular structures is apparently
| | hard for SGMLers when they have only learned to think of them in
| | "See Figure 1" terms.
| +---------------
| *ROTFLMAO!*  Yes, I know what you mean, but... Does "See Figure 1"
| have the same alternate meaning for you guys over there as it does
| around here?!?  ;-}  ;-}

  Yes, and it was intentional.  (I always appreciate it when people "get"
  such jokes.)  I initially wrote "See Chapter 42" but that was hackneyed
  and not entertaining at all.

Erik Naggum, Oslo, Norway

Act from reason, and failure makes you rethink and study harder.
Act from faith, and failure makes you blame someone and push harder.