3 basic XML questions on: non-determism, reserved symbols, and xml:lang

["Roger L. Costello" <costello@mitre.org>]

Hi Folks,

I have three basic XML questions:

[1] It was my understanding that the following is not allowed:

     <!ELEMENT signature (name | (name, date))>

because it would require an XML Parser to "look-ahead" when it
encountered the <name> element to determine which choice was taken.

I have actually tested this example with xerces and XML Spy.  Both
parsers accept this.  Are they erroneously accepting this?  Can someone
please clarify what it means that non-deterministic content models are
not allowed in XML?

[2] It was also my understanding that the following symbols are
"reserved", and may not be used in an instance document's data:

     <  >  &  "  '

Instead, the "escaped" version must be used:

   &lt;  &gt;  &amp;  &quot;  &apos;

However, my experience is that XML Parsers do not require >, ", or ' to
be escaped.  Can someone please clarify what are the "reserved"
symbols?  When do I need to escape >, ", and '?

[3] The purpose of xml:lang is to indicate the language of the contents
of an element.  It was my understanding that xml:lang is a "standard"
attribute that may be used on any element.  However, I have found that
whenever xml:lang is used on an element it must be declared in the DTD. 
How can it be "standard" if it has to be declared?  I guess that
"standard" does not mean "built-in"?

Thanks!  /Roger