HTML specification describes form encoding as: application/x-www-form-urlencoded Forms submitted with this content type must be encoded as follows:

• Control names and values are escaped. Space characters are replaced by '+', and then reserved characters are escaped as described in RFC1738, section 2.2: Non-alphanumeric characters are replaced by '%HH', a percent sign and two hexadecimal digits representing the ASCII code of the character
• The control names/values are listed in the order they appear in the document. The name is separated from the value by '=' and name/value pairs are separated from each other by '&'.