We have the document "Hypertext Markup Language" dated 13 July 1993, and
we have a question about HTML markup. We are working on translating
different sorts of documents to HTML and would like to include some markup
that is not standard HTML and are wondering how other HTML parsers will
regard this markup. We are hoping that they will ignore unrecognizable
markup and not have a serious problem with it. Otherwise, this markup will
have to be included as comments <! ... > with > and < as appropriate.
Most browsers ignore non-HTML tags, but they may gag on some of them.
Including non-HTML tags in the markup is therefore probably not a good idea.
NCSA Mosaic 2.0.0a8 for example gags even on some 100% valid HTML
files (eg http://www.ucc.ie/info/net/htmldoc.html)
For example, HTML can encode bold and italics, but does not handle
underlines. So, if we put as markup:
<UNDERLINE> ..underlined text... </UNDERLINE>
would an HTML parser be able to ignore the <UNDERLINE> and the </UNDERLINE>
and still display the ...underlined text... ?
No. If <underline> is invalid HTML, then neither browser nor parser
will be able to make anything of it unless a browser implements it
Or, does this have to be:
<!<UNDERLINE> ..underlined text... </UNDERLINE>>
A comment must be in the form <!-- text --> so you would have to put
<!-- <underline> etc etc -->
Strictly you ought to be able to say
<!-- <underline>some text</underline> -->
but many browsers will gag on this also.