Reference: http://www.w3.org/TR/REC-html40/charset.html

Encodings from Get use ASCII Hexadecimal Representation

In the URL, keywords are seperated with plus signs ("+"). Real spaces, plus signs, and other illegal characters [who defines illegal characters?] are represented as hexadecimal ASCII escape sequences (%##, e.g., space = %20, plus = %2B) (reference)
hello å there Α

Hexadecimal Representation

space = " " = " ", plus = "+" = "+", > = ">" = > 水 is chinese character for water

Decimal Representation

space = " " = " ", plus = "+" = "+", > = "&62;" = ">"