The boolean values returned by the API isn't very intuitive for use:
For example, the subpages boolean.
For XML: http://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=namespaces%7cnamespacealiases&format=xmlfm
For PHP: http://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=namespaces%7cnamespacealiases&format=phpfm
Can be seen better in DBG: http://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=namespaces%7cnamespacealiases&format=dbgfm
For JSON:
http://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=namespaces%7cnamespacealiases&format=jsonfm
For YAML:
http://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=namespaces%7cnamespacealiases&format=yamlfm
For WDDX:
http://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=namespaces%7cnamespacealiases&format=wddxfm
For all of them boolean values are represented as a empty string rather than an intuitive boolean value.
For PHP and JS the best output would be true/false rather than a string you need to explicitly test for.
I don't know much about YAML.
As for WDDX, even just looking at the output it should be apparent that there should be a boolean type that the API should be outputting.
And even XML doesn't follow a proper standard, even if you go by the normal 'boolean' type use inside of (X)HTML for checkboxes and selects, the proper output should be subpages="subpages" for true.
In some languages it may even be possible for errors to come out of trying to use the data in a simple format if you don't add a bunch of unnecessary cruft to your code to explicitly test for the unintuitive output.
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