xml modeling

3.26: adda/xml modeling:
. the basics of xml started with
putting "(br) -- line break -- in angle-brackets;
because, angle brackets classically mean
a formal parameter,
as seen in language syntax diagrams .
. this formalism was required because
-- despite their being a standard for text --
there was no unambiguous representation for
line structure: { cr, lf, cr-lf, line's char count } .
. another (incidental) property was that
angle brackets were separating text that was
not meant to be taken literally;
and, this was the basis for
extending the use of angle brackets
for any text that was not to be taken literally .
. the basic structure of {sgml, html, xml}
is to have a pair of angle brackets for
each opening and closing element .
. using that way, there's a restriction on
literal text containing angle brackets;
whereas,
with a parenthetical method (described next)
there's a restriction only on
un-paired parentheses, and the use of the
code-starting symbol: [!]
which can be chosen to be both
very rare in literal text
and easy to write, read, and find .
. the math-english way would have made use
of parenthetical symbols:
{literal text ...}
[!]
block-name( parameters,,, ):
(
{literal text ...}
)-block-name
[!]
non-block ( parameters,,,)
{literal text ...}
3.31:
. the lisp way is slightly more compact:
{literal text ...}
[!]
(block-name parameters,,, :
{literal text ...}
)-block-name
[!]
(non-block-name parameters,,,)
{literal text ...} .