What is "sgmlguid"

SGMLguid was an early SGML application used at CERN that was the original inspiration of HTML. Because SGMLguid files were commonly named with .sgml as a file extension, it has sometimes been confused with SGML itself, which is why SGML has sometimes been incorrectly cited as the predecessor of HTML, while, in fact, SGMLguid and HTML are both SGML applications.