BS4 drops '?' from processing instructions

[Andrew Mercer]

Running the following script:
    import bs4
    xml = '<?xml version="1.0" encoding="utf-8"?><p>Test xml with PI <?dtall break="line"?>a..z<?dtall break="line"?></p>'
    soup = bs4.BeautifulSoup(xml, 'xml')
    str(soup)

Produces the following output:
    '<?xml version="1.0" encoding="utf-8"?>\n<p>Test xml with PI <?dtall break="line">a..z<?dtall break="line"></p>'

The closing ? has been stripped from the <?dtall ... ?> tags.

OS: Windows 7
Python 3.4.3
Parser lxml 3.4.4

[Andrew Mercer (akmercer)]

I believe the following needs to be changed in element.py"

class ProcessingInstruction(PreformattedString):

    PREFIX = '<?'
    SUFFIX = '>'

should be

class ProcessingInstruction(PreformattedString):

    PREFIX = '<?'
    SUFFIX = '?>'

[Leonard Richardson (leonardr)]

SGML (HTML) processing instructions look like this: <?foo>
XML processing instructions look like this: <?foo?>

Beautiful Soup handles SGML processing instructions correctly but not XML processing instructions. Revision 399 makes sure that when a document is parsed as XML the processing instructions are treated as XML processing instructions.