Seeking clarification-- NET tags

Murray Maloney <murray@oclc.org>
Date: Thu, 16 Jun 94 12:33:56 EDT
Message-id: <9406161210.aa11345@dali.scocan.sco.COM>
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From: Murray Maloney <murray@oclc.org>
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Subject: Seeking clarification-- NET tags
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Please clarify for me:

NOTE: SHORTTAG

The SGML declaration for HTML specifies SHORTTAG YES , which means
that there are some other valid syntaxes for tags, e.g. NET tags: <em/.../ ,
empty start tags: <> , empty end tags: </> . Until such time as support for
these idioms is widely deployed, their use is strongly discouraged. 


What are NET tags?  What does <em/.../ signify?