in reply to Tokenizing XML

The comment matching subexpression is way too liberal. How it really works is that <! opens a markup declaration, and within such, a -- double dash starts a comment and another one terminates the comment. In other words, <!-----> (5 dashes) cannot be part of a well-formed document: <! starts the declaration, -- starts a comment, -- closes it, but then there’s an extraneous - dash which is outside the comment and is a markup declaration syntax error. OTOH, <!------> (6 dashes) is fine, except it will comment out much more than you think, because the first 4 dashes open an close an empty comment, and then the last two dashes open a comment that is not closed at this point. However, if you write something like <!--- --> (3 dashes, space, 2 dashes), that’s fine: the first 2 dashes open the comment, the next dash is lone so it’s part of the comment (along with the space that follows), and the last 2 dashes close the comment.

Likewise, your parsing for the XML PI is too simpleminded; additionally, you have no provision for parsing other kinds of PIs at all.

You may have more errors; I didn’t look any harder than that.

You’d do well to just read the spec; it really isn’t prohibitively big or difficult to understand, and if you want to write a correct parser, there’s no way around it.

Because despite claims to the contrary, what you’re doing is parsing. And regexen are certainly a fine tool to do that. The oft-repeated advice is because people who use regexen usually don’t actually parse, and in general, do not have a task that merits the effort required to write a complete, correct parser on their own either, so telling them to use an existing parser is exactly what they need.

Makeshifts last the longest.

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Re^2: Tokenizing XML
by eric256 (Parson) on Dec 26, 2005 at 21:15 UTC

    Hmmm I was playing with the comment sub expression and I think this might work (dunno, i played with look aheads but those arn't realy my speciality. ;))

    my $test = qr/(<!--(?:[-][^-]|[^-])*-->)/;

for ( "<!-- -->", "<!----->", "<!--- -->", "<!---->" , "<!-- - -- -->"
+) {
    print $_, ($_ =~ $test ? "ok": "fail"),"\n";
}

    [download]

    So it should match anything that looks like a comment and the only tuime it has two dashes in a row is at the begging and at the end. Needs mroe vigerous testing though.


    ___________
    Eric Hodges
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Re^2: Tokenizing XML
by Skeeve (Parson) on Dec 26, 2005 at 23:35 UTC

    You say:

    OTOH, (6 dashes) is fine,

    I did what you told me and took a look at the W3C recommendations and it says:
    the string "--" (double-hyphen) MUST NOT occur within comments.
    So I think, this should do for a legal comment:
    <!--(?:[^-]|-[^-])*-->

    s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
    +.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e
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      With six dashes it doesn’t occur within comments: six dashes mean one complete (empty) comment (the first 4 dashes) and one open comment that stretches past the angle bracket (the next 2 dashes). 8 dashes in a row would be valid and do what you expect (because they indicate 2 empty comments, both closed). So sequences of 4 dashes do no cause confusion. Neither do sequences of 5 dashes, provided that a 5-dash-sequence is followed by a non-dash character.

      Your regex will reject valid comments.

      Ok, turns out that I’m applying SGML rules and that they have been simplified for XML. I guess I should have another read over the spec myself, sigh. That regex should work then.

      Makeshifts last the longest.

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