Re-serializing query parsed with HttpUtility.ParseQueryString() has confusing, undocumented behavior

[JLRishe]

The HttpUtility.ParseQueryString() method returns a NameValueCollection that can be modified and then converted back to a string to produce a new query string.

However, the behavior of the .ToString() method that produces that string varies based on app settings and execution environment:

• Under some circumstances, keys and values are escaped using HttpUtility.UrlEncodeUnicode(), which encodes ® as %u00ae (unicode encoding)
• Under other circumstances, keys and values are escaped using HttpUtility.UrlEncode(), which encodes ® as %c2%ae (UTF8 encoding)

// q is either "a=%c2%a9&b=%c2%ae" or "a=%u00a9&b=%u00ae" 
var q = HttpUtility.ParseQueryString("a=%c2%a9&b=%c2%ae").ToString();

To the best of my understanding, this behavior is determined as follows:

• If the app has an appSetting with key aspnet:DontUsePercentUUrlEncoding and value true or false, then it will use UTF8 encoding for true and unicode encoding for false
• Otherwise, if it is an ASP.NET app with a targetFramework of 4.5.2+ in its web.config, it will use UTF8 encoding
  • I'm not sure in what way this applies to ASP.NET Core apps, or if other factors are taken into account in determining the target framework
• Otherwise, it will use unicode encoding

Clearly this behavior is quite confusing, and as far as I can tell, there is no documentation on it. I think it would be ideal if this were documented.

I would be happy to submit a pull request for the HttpUtility.ParseQueryString documentation, but I am not clear on the full nuances of this behavior, and am not sure what would be the best way to describe it in the documentation. I would be grateful if someone could give me a push in the right direction.

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