updated testcase

Entering into http://html5.validator.nu/ the first example
    <p>123<p>abcdefg</p>456</p>
gives
    Error: No p element in scope but a p end tag seen.
    From line 1, column 24; to line 1, column 27
    efg</p>456</p>↩

because the </p> at the end doesn't close a tag.  The second <p> closes the 
first <p> per HTML5 parsing rules.
http://www.whatwg.org/specs/web-apps/current-work/multipage/tree-construction.ht
ml#parsing-main-inbody says

"""
A start tag whose tag name is one of: "address", "article", "aside", 
"blockquote", "center", "details", "dialog", "dir", "div", "dl", "fieldset", 
"figcaption", "figure", "footer", "header", "hgroup", "main", "menu", "nav", 
"ol", "p", "section", "summary", "ul"
If the stack of open elements has a p element in button scope, then act as if 
an end tag with the tag name "p" had been seen.

Insert an HTML element for the token.
"""

which means that when a <p> is seen inside a <p>, an implicit </p> is seen, so
    <p>123<p>abcdefg</p>456</p>
is equivalent to
    <p>123</p><p>abcdefg</p>456

which is what the HTML sanitizer produces.

By understanding browser tag nesting rules, the sanitizer avoids a lot of 
ambiguity in HTML, and can produce output that will be consistently and safely 
interpreted by a variety of browsers.

----

Sanitizers.BLOCKS.sanitize("<div><meta/><p>abcdefg</p></div>")

should not produce

"<div><meta/><p>abcdefg</p></div>"

since <meta> is not a block tag, and is not even allowed in the body.

----

Marking this bug invalid.  Please reopen if you feel this was in error.

The paragraph handling has just been added to illustrate the sanitizers 
behaviour.

However, the meta-tag is a real problem for us as thunderbird generates markup 
like "<blockquote><meta></blockquote>" all the time and we have to display this 
for our users correctly. However, this becomes hard because the sanitizer 
modifies the markup during the removal of the meta-tag. I just want the 
sanitizer to remove the meta-tag which is currently not possible.

Please reopen as I'm not allowed to...

Kind regards
Matthias

Reopened.

Is the problem that you're doing something like

    PolicyFactory policy = new HtmlPolicyBuilder()
      .allowCommonBlockElements()
      .allowElements("meta")
      .toFactory();
     String htmlSnippet = "<blockquote><meta></blockquote>";
     String sanitized = policy.sanitize(htmlSnippet);
     System.out.println(sanitized);

and you get

    <blockquote></blockquote></body><meta />

?

Closing for lack of response.  Re the attached test case:

> assertEquals("<p>123<p>abcdefg</p>456</p>",
>                     
Sanitizers.BLOCKS.sanitize("<p>123<p>abcdefg</p>456</p>"));

the test golden is invalid.  <p> tags do not nest in HTML.

> assertEquals("<div><meta/><p>abcdefg</p></div>",
>                     
Sanitizers.BLOCKS.sanitize("<div><meta/><p>abcdefg</p></div>"));

is also invalid since <p> tags cannot be direct children of <div> elements.
You can white-list <meta> elements if you like using a custom policy, but 
<meta> is not a block element so should be Sanitizers.BLOCKS.

Hello everyone!

We have a similar behaviour in this case:
assertEquals("<h1>TEXT</h1>", 
Sanitizers.BLOCKS.sanitize("<H1><center>TEXT</H1>"));

For this one the result is:
<h1></h1>TEXT
instead of:
<h1>TEXT</h1>

But test case:
assertEquals("<h1>TEXT</h1>", 
Sanitizers.BLOCKS.sanitize("<H1></center>TEXT</H1>"));

works as expected:
<h1>TEXT</h1>

What's wrong with the first one?

I would appreciate your feedback to this case.

#6, filed as 
https://code.google.com/p/owasp-java-html-sanitizer/issues/detail?id=33

I am facing similar issue with <font> along with <div>.
<div> along with its content is moved outside <font>.
Due to this <font> is not applied to the content in <div>.

PolicyFactory policy = new HtmlPolicyBuilder()
            .allowCommonBlockElements()
            .allowElements("font")
            .allowAttributes("face", "size").onElements("font")
            .toFactory();
        String htmlSnippet = "<font face=\"Calibri\" size=\"2\"><div>Hi Hari</div></font>";
        String sanitized = policy.sanitize(htmlSnippet);

Original:
<font face="Calibri" size="2"><div>Hi Hari</div></font>

Sanitized:
<font face="Calibri" size="2"></font><div>Hi Hari</div>