Re: "--" question

> I am guessing that in SGML a bare "--" can be considered markup.

SGML comments can be embedded inside decarations so

<!ENTITY nbsp "&#160;" -- a non breaking space -->


for example.

or even

<!ENTITY -- a keyword -- nbsp  -- a name --"&#160;" -- a non breaking space -->


The classic one is

<!---------!>

which is legal SGML comment if there is a multiple of four - as if there
are 4n - then this is an empty declaration with n empty comments.
Otherwise it's an error as the declaration would be ill formed.

XML banned nested comments so you have to have

<!ENTITY nbsp "&#160;"--><!-- non breaking space -->

but banned -- appearing in comments to ensure that every legal XML
comment
was a legal SGML one, and more generally to ensure every XML document
was an (WWW-)SGML one.

David

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