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W3 Markup Validator Instructions 
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The W3 Markup Validator takes in 3 forms of input for validation. We
only focus on two, file upload and direct input. Feel free to use
either.

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To check that your results are well-formed:
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1. Copy your results into the input form under the direct input tab, 
or save your results to a file and select this file under the file upload tab.
Make sure your copied results include an XML declaration at the top: 
<?xml version="1.0" encoding="UTF-8"?>
(XQuery automatically prints this at the beginning of your query results,
just make sure that you copy it)

2. Click on the "check" button. You will see a red bar if there were errors,
and a green bar if the check was successful (no errors, but there may still be
warnings). The errors and warnings will be at the bottom of the page.

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To check that your results follow a given DTD:
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Follow instructions above. In addition, add a DOCTYPE declaration after the
XML declaration and before the rest of the XML content in the following form:

<!DOCTYPE [name of root element as specified by DTD] [
...
[rules of DTD as specified for the problem]
...
]>

For example, the following would be a DOCTYPE declaration for problem 1:

<!DOCTYPE result [
<!ELEMENT result (country)>
<!ELEMENT country (name, city+)>
<!ELEMENT city (name)>
<!ELEMENT name (#PCDATA)>
]>

The rules are a copy of the DTD specified for problem 1.