when this - obviously correct html - is parsed:

<a href=mailto:xyz@domain.com>xyz</a>

this exception is raised:
HTMLParseError: junk characters in start 
tag: '@domain.com>', at line 1, column 1

I work around this by adding '@' to the
allowed character's class:

import HTMLParser
HTMLParser.attrfind = re.compile(
    r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
    r'(\'[^\']*\'|"[^"]*"|[-a-zA-Z0-9./,:;+*%?!&$\(\)
_#=~@]*))?')

myparser = HTMLParser.HTMLParser()
myparser.feed('<a ... ')

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I don't believe this HTML is obviously correct.  
The section on attributes in the HTML 4.01 Recommendation
(http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.2.2) says:

In certain cases, authors may specify the value of an
attribute without any quotation marks. The attribute value
may only contain letters (a-z and A-Z), digits (0-9),
hyphens (ASCII decimal 45), periods (ASCII decimal 46),
underscores (ASCII decimal 95), and colons (ASCII decimal
58). We recommend using quotation marks even when it is
possible to eliminate them.  

The regex is already more liberal than this, allowing slashes
and various other symbols, so we might as well add '@', but
you should also consider adding quotation marks to the
original attribute.

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Committed to the CVS HEAD; thanks!

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see request #1046092 to fix it